Add latest changes from gitlab-org/gitlab@master

9 files changed, 368 insertions, 216 deletions

diff --git a/spec/tooling/lib/tooling/find_changes_spec.rb b/spec/tooling/lib/tooling/find_changes_spec.rb
index 3616732e328..5932eb5e919 100644
--- a/spec/tooling/lib/tooling/find_changes_spec.rb
+++ b/spec/tooling/lib/tooling/find_changes_spec.rb
@@ -3,57 +3,66 @@
 require_relative '../../../../tooling/lib/tooling/find_changes'
 require_relative '../../../support/helpers/stub_env'
 require 'json'
+require 'tempfile'
 
 RSpec.describe Tooling::FindChanges, feature_category: :tooling do
   include StubENV
 
+  attr_accessor :changed_files_file, :predictive_tests_file, :frontend_fixtures_mapping_file
+
   let(:instance) do
-    described_class.new(
-      output_file: output_file,
-      matched_tests_file: matched_tests_file,
-      frontend_fixtures_mapping_path: frontend_fixtures_mapping_path
-    )
+    described_class.new(changed_files_pathname, predictive_tests_pathname, frontend_fixtures_mapping_pathname)
   end
 
-  let(:gitlab_client)                  { double('GitLab') } # rubocop:disable RSpec/VerifiedDoubles
-  let(:output_file)                    { 'output.txt' }
-  let(:output_file_content)            { 'first_file second_file' }
-  let(:matched_tests_file)             { 'matched_tests.txt' }
-  let(:frontend_fixtures_mapping_path) { 'frontend_fixtures_mapping.json' }
-  let(:file_changes)                   { ['file1.rb', 'file2.rb'] }
+  let(:changed_files_pathname)             { changed_files_file.path }
+  let(:predictive_tests_pathname)          { predictive_tests_file.path }
+  let(:frontend_fixtures_mapping_pathname) { frontend_fixtures_mapping_file.path }
+  let(:gitlab_client)                      { double('GitLab') } # rubocop:disable RSpec/VerifiedDoubles
+
+  around do |example|
+    self.changed_files_file             = Tempfile.new('changed_files_file')
+    self.predictive_tests_file          = Tempfile.new('predictive_tests_file')
+    self.frontend_fixtures_mapping_file = Tempfile.new('frontend_fixtures_mapping_file')
+
+    # See https://ruby-doc.org/stdlib-1.9.3/libdoc/tempfile/rdoc/
+    #     Tempfile.html#class-Tempfile-label-Explicit+close
+    begin
+      example.run
+    ensure
+      frontend_fixtures_mapping_file.close
+      frontend_fixtures_mapping_file.unlink
+      predictive_tests_file.close
+      predictive_tests_file.unlink
+      changed_files_file.close
+      changed_files_file.unlink
+    end
+  end
 
   before do
     stub_env(
       'CI_API_V4_URL' => 'gitlab_api_url',
       'CI_MERGE_REQUEST_IID' => '1234',
       'CI_MERGE_REQUEST_PROJECT_PATH' => 'dummy-project',
-      'PROJECT_TOKEN_FOR_CI_SCRIPTS_API_USAGE' => 'dummy-token',
-      'RSPEC_TESTS_MAPPING_PATH' => '/tmp/does-not-exist.out'
+      'PROJECT_TOKEN_FOR_CI_SCRIPTS_API_USAGE' => 'dummy-token'
     )
 
     allow(instance).to receive(:gitlab).and_return(gitlab_client)
-    allow(File).to receive(:exist?).and_call_original
-    allow(File).to receive(:read).and_call_original
-    allow(File).to receive(:write)
   end
 
   describe '#execute' do
     subject { instance.execute }
 
-    context 'when there is no output file' do
-      let(:output_file) { nil }
+    context 'when there is no changed files file' do
+      let(:changed_files_pathname) { nil }
 
       it 'raises an ArgumentError' do
-        expect { subject }.to raise_error(ArgumentError, "An path to an output file must be given as first argument.")
+        expect { subject }.to raise_error(
+          ArgumentError, "A path to the changed files file must be given as first argument."
+        )
       end
     end
 
-    context 'when an output file is provided' do
-      before do
-        allow(File).to receive(:exist?).with(output_file).and_return(true)
-        allow(File).to receive(:read).with(output_file).and_return(output_file_content)
-      end
-
+    context 'when an changed files file is provided' do
       it 'does not call GitLab API to retrieve the MR diff' do
         expect(gitlab_client).not_to receive(:merge_request_changes)
 
@@ -61,64 +70,57 @@ RSpec.describe Tooling::FindChanges, feature_category: :tooling do
       end
 
       context 'when there are no file changes' do
-        let(:output_file_content) { '' }
-
-        it 'writes an empty string to output file' do
-          expect(File).to receive(:write).with(output_file, '')
-
-          subject
+        it 'writes an empty string to changed files file' do
+          expect { subject }.not_to change { File.read(changed_files_pathname) }
         end
       end
 
       context 'when there are file changes' do
-        let(:output_file_content) { 'first_file_changed second_file_changed' }
+        before do
+          File.write(changed_files_pathname, changed_files_file_content)
+        end
 
-        it 'writes file changes to output file' do
-          expect(File).to receive(:write).with(output_file, output_file_content)
+        let(:changed_files_file_content) { 'first_file_changed second_file_changed' }
 
-          subject
+        # This is because we don't have frontend fixture mappings: we will just write the same data that we read.
+        it 'does not change the changed files file' do
+          expect { subject }.not_to change { File.read(changed_files_pathname) }
         end
       end
 
       context 'when there is no matched tests file' do
-        let(:matched_tests_file) { '' }
-
-        it 'does not add frontend fixtures mapping to the output file' do
-          expect(File).to receive(:write).with(output_file, output_file_content)
+        let(:predictive_tests_pathname) { nil }
 
-          subject
+        it 'does not add frontend fixtures mapping to the changed files file' do
+          expect { subject }.not_to change { File.read(changed_files_pathname) }
         end
       end
 
       context 'when there is no frontend fixture files' do
-        let(:frontend_fixtures_mapping_path) { '' }
+        let(:frontend_fixtures_mapping_pathname) { nil }
 
-        it 'does not add frontend fixtures mapping to the output file' do
-          expect(File).to receive(:write).with(output_file, output_file_content)
-
-          subject
+        it 'does not add frontend fixtures mapping to the changed files file' do
+          expect { subject }.not_to change { File.read(changed_files_pathname) }
         end
       end
 
       context 'when the matched tests file and frontend fixture files are provided' do
         before do
-          allow(File).to receive(:exist?).with(matched_tests_file).and_return(true)
-          allow(File).to receive(:exist?).with(frontend_fixtures_mapping_path).and_return(true)
-
-          allow(File).to receive(:read).with(matched_tests_file).and_return(matched_tests)
-          allow(File).to receive(:read).with(frontend_fixtures_mapping_path).and_return(frontend_fixtures_mapping_json)
+          File.write(predictive_tests_pathname, matched_tests)
+          File.write(frontend_fixtures_mapping_pathname, frontend_fixtures_mapping_json)
+          File.write(changed_files_pathname, changed_files_file_content)
         end
 
+        let(:changed_files_file_content) { '' }
+
         context 'when there are no mappings for the matched tests' do
           let(:matched_tests) { 'match_spec1 match_spec_2' }
           let(:frontend_fixtures_mapping_json) do
             { other_spec: ['other_mapping'] }.to_json
           end
 
-          it 'does not add frontend fixtures mapping to the output file' do
-            expect(File).to receive(:write).with(output_file, output_file_content)
-
-            subject
+          it 'does not change the changed files file' do
+            expect { subject }.not_to change { File.read(changed_files_pathname) }
           end
         end
 
@@ -129,10 +131,20 @@ RSpec.describe Tooling::FindChanges, feature_category: :tooling do
             { match_spec1: spec_mappings }.to_json
           end
 
-          it 'adds the frontend fixtures mappings to the output file' do
-            expect(File).to receive(:write).with(output_file, "#{output_file_content} #{spec_mappings.join(' ')}")
+          context 'when the changed files file is initially empty' do
+            it 'adds the frontend fixtures mappings to the changed files file' do
+              expect { subject }.to change { File.read(changed_files_pathname) }.from('').to(spec_mappings.join(' '))
+            end
+          end
+
+          context 'when the changed files file is initially not empty' do
+            let(:changed_files_file_content) { 'initial_content1 initial_content2' }
 
-            subject
+            it 'adds the frontend fixtures mappings to the changed files file' do
+              expect { subject }.to change { File.read(changed_files_pathname) }
+                .from(changed_files_file_content)
+                .to("#{changed_files_file_content} #{spec_mappings.join(' ')}")
+            end
           end
         end
       end
@@ -155,15 +167,9 @@ RSpec.describe Tooling::FindChanges, feature_category: :tooling do
     end
 
     context 'when a file is passed as an argument' do
-      let(:output_file) { 'output_file.out' }
-
-      it 'does not read the output file' do
-        expect(File).not_to receive(:read).with(output_file)
-
-        subject
-      end
+      let(:changed_files_pathname) { 'does-not-exist.out' }
 
-      it 'calls GitLab API anyways' do
+      it 'calls GitLab API' do
         expect(gitlab_client).to receive(:merge_request_changes)
         .with('dummy-project', '1234')
 
diff --git a/spec/tooling/lib/tooling/find_tests_spec.rb b/spec/tooling/lib/tooling/find_tests_spec.rb
index e531fb9548e..905f81c4bbd 100644
--- a/spec/tooling/lib/tooling/find_tests_spec.rb
+++ b/spec/tooling/lib/tooling/find_tests_spec.rb
@@ -7,27 +7,29 @@ require_relative '../../../support/helpers/stub_env'
 RSpec.describe Tooling::FindTests, feature_category: :tooling do
   include StubENV
 
-  attr_accessor :changes_file, :matching_tests_paths
+  attr_accessor :changed_files_file, :predictive_tests_file
 
-  let(:instance)                     { described_class.new(changes_file, matching_tests_paths) }
+  let(:instance)                     { described_class.new(changed_files_pathname, predictive_tests_pathname) }
   let(:mock_test_file_finder)        { instance_double(TestFileFinder::FileFinder) }
   let(:new_matching_tests)           { ["new_matching_spec.rb"] }
-  let(:changes_file_content)         { "changed_file1 changed_file2" }
-  let(:matching_tests_paths_content) { "previously_matching_spec.rb" }
+  let(:changed_files_pathname)       { changed_files_file.path }
+  let(:predictive_tests_pathname)    { predictive_tests_file.path }
+  let(:changed_files_content)        { "changed_file1 changed_file2" }
+  let(:predictive_tests_content)     { "previously_matching_spec.rb" }
 
   around do |example|
-    self.changes_file         = Tempfile.new('changes')
-    self.matching_tests_paths = Tempfile.new('matching_tests')
+    self.changed_files_file    = Tempfile.new('changed_files_file')
+    self.predictive_tests_file = Tempfile.new('predictive_tests_file')
 
     # See https://ruby-doc.org/stdlib-1.9.3/libdoc/tempfile/rdoc/
     #     Tempfile.html#class-Tempfile-label-Explicit+close
     begin
       example.run
     ensure
-      changes_file.close
-      matching_tests_paths.close
-      changes_file.unlink
-      matching_tests_paths.unlink
+      changed_files_file.close
+      predictive_tests_file.close
+      changed_files_file.unlink
+      predictive_tests_file.unlink
     end
   end
 
@@ -42,44 +44,44 @@ RSpec.describe Tooling::FindTests, feature_category: :tooling do
     )
 
     # We write into the temp files initially, to later check how the code modified those files
-    File.write(changes_file, changes_file_content)
-    File.write(matching_tests_paths, matching_tests_paths_content)
+    File.write(changed_files_pathname, changed_files_content)
+    File.write(predictive_tests_pathname, predictive_tests_content)
   end
 
   describe '#execute' do
     subject { instance.execute }
 
-    context 'when the matching_tests_paths file does not exist' do
-      let(:instance)                 { described_class.new(non_existing_output_file, matching_tests_paths) }
-      let(:non_existing_output_file) { 'tmp/another_file.out' }
+    context 'when the predictive_tests_pathname file does not exist' do
+      let(:instance) { described_class.new(non_existing_output_pathname, predictive_tests_pathname) }
+      let(:non_existing_output_pathname) { 'tmp/another_file.out' }
 
       around do |example|
         example.run
       ensure
-        FileUtils.rm_rf(non_existing_output_file)
+        FileUtils.rm_rf(non_existing_output_pathname)
       end
 
       it 'creates the file' do
-        expect { subject }.to change { File.exist?(non_existing_output_file) }.from(false).to(true)
+        expect { subject }.to change { File.exist?(non_existing_output_pathname) }.from(false).to(true)
       end
     end
 
-    context 'when the matching_tests_paths file already exists' do
+    context 'when the predictive_tests_pathname file already exists' do
       it 'does not create an empty file' do
-        expect(File).not_to receive(:write).with(matching_tests_paths, '')
+        expect(File).not_to receive(:write).with(predictive_tests_pathname, '')
 
         subject
       end
     end
 
     it 'does not modify the content of the input file' do
-      expect { subject }.not_to change { File.read(changes_file) }
+      expect { subject }.not_to change { File.read(changed_files_pathname) }
     end
 
     it 'does not overwrite the output file' do
-      expect { subject }.to change { File.read(matching_tests_paths) }
-                        .from(matching_tests_paths_content)
-                        .to("#{matching_tests_paths_content} #{new_matching_tests.uniq.join(' ')}")
+      expect { subject }.to change { File.read(predictive_tests_pathname) }
+                        .from(predictive_tests_content)
+                        .to("#{predictive_tests_content} #{new_matching_tests.uniq.join(' ')}")
     end
 
     it 'loads the tests.yml file with a pattern matching mapping' do
@@ -148,8 +150,8 @@ RSpec.describe Tooling::FindTests, feature_category: :tooling do
       it 'writes uniquely matching specs to the output' do
         subject
 
-        expect(File.read(matching_tests_paths).split(' ')).to match_array(
-          matching_tests_paths_content.split(' ') + new_matching_tests.uniq
+        expect(File.read(predictive_tests_pathname).split(' ')).to match_array(
+          predictive_tests_content.split(' ') + new_matching_tests.uniq
         )
       end
     end
diff --git a/spec/tooling/lib/tooling/helpers/file_handler_spec.rb b/spec/tooling/lib/tooling/helpers/file_handler_spec.rb
index 7c8310c4bd9..d6f68baeb90 100644
--- a/spec/tooling/lib/tooling/helpers/file_handler_spec.rb
+++ b/spec/tooling/lib/tooling/helpers/file_handler_spec.rb
@@ -42,18 +42,18 @@ RSpec.describe Tooling::Helpers::FileHandler, feature_category: :tooling do
     subject { instance.read_array_from_file(input_file_path) }
 
     context 'when the input file does not exist' do
-      let(:non_existing_input_file) { 'tmp/another_file.out' }
+      let(:non_existing_input_pathname) { 'tmp/another_file.out' }
 
-      subject { instance.read_array_from_file(non_existing_input_file) }
+      subject { instance.read_array_from_file(non_existing_input_pathname) }
 
       around do |example|
         example.run
       ensure
-        FileUtils.rm_rf(non_existing_input_file)
+        FileUtils.rm_rf(non_existing_input_pathname)
       end
 
       it 'creates the file' do
-        expect { subject }.to change { File.exist?(non_existing_input_file) }.from(false).to(true)
+        expect { subject }.to change { File.exist?(non_existing_input_pathname) }.from(false).to(true)
       end
     end
 
@@ -67,9 +67,10 @@ RSpec.describe Tooling::Helpers::FileHandler, feature_category: :tooling do
   end
 
   describe '#write_array_to_file' do
-    let(:content_array) { %w[new_entry] }
+    let(:content_array)  { %w[new_entry] }
+    let(:overwrite_flag) { false }
 
-    subject { instance.write_array_to_file(output_file_path, content_array) }
+    subject { instance.write_array_to_file(output_file_path, content_array, overwrite: overwrite_flag) }
 
     context 'when the output file does not exist' do
       let(:non_existing_output_file) { 'tmp/another_file.out' }
@@ -93,6 +94,14 @@ RSpec.describe Tooling::Helpers::FileHandler, feature_category: :tooling do
       it 'writes the correct content to the file' do
         expect { subject }.to change { File.read(output_file_path) }.from('').to(content_array.join(' '))
       end
+
+      context 'when the content array is not sorted' do
+        let(:content_array) { %w[new_entry a_new_entry] }
+
+        it 'sorts the array before writing it to file' do
+          expect { subject }.to change { File.read(output_file_path) }.from('').to(content_array.sort.join(' '))
+        end
+      end
     end
 
     context 'when the output file is not empty' do
@@ -100,8 +109,18 @@ RSpec.describe Tooling::Helpers::FileHandler, feature_category: :tooling do
 
       it 'appends the correct content to the file' do
         expect { subject }.to change { File.read(output_file_path) }
-        .from(initial_content)
-        .to((initial_content.split(' ') + content_array).join(' '))
+          .from(initial_content)
+          .to((initial_content.split(' ') + content_array).join(' '))
+      end
+
+      context 'when the overwrite flag is set to true' do
+        let(:overwrite_flag) { true }
+
+        it 'overwrites the previous content' do
+          expect { subject }.to change { File.read(output_file_path) }
+            .from(initial_content)
+            .to(content_array.join(' '))
+        end
       end
     end
   end
diff --git a/spec/tooling/lib/tooling/mappings/graphql_base_type_mappings_spec.rb b/spec/tooling/lib/tooling/mappings/graphql_base_type_mappings_spec.rb
index 521958573fd..b6459428214 100644
--- a/spec/tooling/lib/tooling/mappings/graphql_base_type_mappings_spec.rb
+++ b/spec/tooling/lib/tooling/mappings/graphql_base_type_mappings_spec.rb
@@ -6,11 +6,17 @@ require_relative '../../../../../tooling/lib/tooling/mappings/graphql_base_type_
 RSpec.describe Tooling::Mappings::GraphqlBaseTypeMappings, feature_category: :tooling do
   # We set temporary folders, and those readers give access to those folder paths
   attr_accessor :foss_folder, :ee_folder, :jh_folder
-  attr_accessor :changes_file, :matching_tests_paths
+  attr_accessor :changed_files_file, :predictive_tests_file
+
+  let(:changed_files_pathname)           { changed_files_file.path }
+  let(:predictive_tests_pathname)        { predictive_tests_file.path }
+  let(:instance)                         { described_class.new(changed_files_pathname, predictive_tests_pathname) }
+  let(:changed_files_content)            { "changed_file1 changed_file2" }
+  let(:predictive_tests_initial_content) { "previously_matching_spec.rb" }
 
   around do |example|
-    self.changes_file         = Tempfile.new('changes')
-    self.matching_tests_paths = Tempfile.new('matching_tests')
+    self.changed_files_file    = Tempfile.new('changed_files_file')
+    self.predictive_tests_file = Tempfile.new('predictive_tests_file')
 
     Dir.mktmpdir('FOSS') do |foss_folder|
       Dir.mktmpdir('EE') do |ee_folder|
@@ -24,20 +30,16 @@ RSpec.describe Tooling::Mappings::GraphqlBaseTypeMappings, feature_category: :to
           begin
             example.run
           ensure
-            changes_file.close
-            matching_tests_paths.close
-            changes_file.unlink
-            matching_tests_paths.unlink
+            changed_files_file.close
+            predictive_tests_file.close
+            changed_files_file.unlink
+            predictive_tests_file.unlink
           end
         end
       end
     end
   end
 
-  let(:instance) { described_class.new(changes_file, matching_tests_paths) }
-  let(:changes_file_content)                 { "changed_file1 changed_file2" }
-  let(:matching_tests_paths_initial_content) { "previously_matching_spec.rb" }
-
   before do
     stub_const("Tooling::Mappings::GraphqlBaseTypeMappings::GRAPHQL_TYPES_FOLDERS", {
       nil => [foss_folder],
@@ -46,23 +48,23 @@ RSpec.describe Tooling::Mappings::GraphqlBaseTypeMappings, feature_category: :to
     })
 
     # We write into the temp files initially, to later check how the code modified those files
-    File.write(changes_file, changes_file_content)
-    File.write(matching_tests_paths, matching_tests_paths_initial_content)
+    File.write(changed_files_pathname, changed_files_content)
+    File.write(predictive_tests_pathname, predictive_tests_initial_content)
   end
 
   describe '#execute' do
     subject { instance.execute }
 
     context 'when no GraphQL files were changed' do
-      let(:changes_file_content) { '' }
+      let(:changed_files_content) { '' }
 
       it 'does not change the output file' do
-        expect { subject }.not_to change { File.read(matching_tests_paths) }
+        expect { subject }.not_to change { File.read(predictive_tests_pathname) }
       end
     end
 
     context 'when some GraphQL files were changed' do
-      let(:changes_file_content) do
+      let(:changed_files_content) do
         [
           "#{foss_folder}/my_graphql_file.rb",
           "#{foss_folder}/my_other_graphql_file.rb"
@@ -76,7 +78,7 @@ RSpec.describe Tooling::Mappings::GraphqlBaseTypeMappings, feature_category: :to
         end
 
         it 'does not change the output file' do
-          expect { subject }.not_to change { File.read(matching_tests_paths) }
+          expect { subject }.not_to change { File.read(predictive_tests_pathname) }
         end
       end
 
@@ -92,9 +94,9 @@ RSpec.describe Tooling::Mappings::GraphqlBaseTypeMappings, feature_category: :to
         end
 
         it 'writes the correct specs in the output' do
-          expect { subject }.to change { File.read(matching_tests_paths) }
-                            .from(matching_tests_paths_initial_content)
-                            .to("#{matching_tests_paths_initial_content} spec/my_graphql_file_spec.rb")
+          expect { subject }.to change { File.read(predictive_tests_pathname) }
+                            .from(predictive_tests_initial_content)
+                            .to("#{predictive_tests_initial_content} spec/my_graphql_file_spec.rb")
         end
       end
     end
@@ -110,7 +112,7 @@ RSpec.describe Tooling::Mappings::GraphqlBaseTypeMappings, feature_category: :to
     end
 
     context 'when no files were changed' do
-      let(:changes_file_content) { '' }
+      let(:changed_files_content) { '' }
 
       it 'returns an empty array' do
         expect(subject).to match_array([])
@@ -118,7 +120,7 @@ RSpec.describe Tooling::Mappings::GraphqlBaseTypeMappings, feature_category: :to
     end
 
     context 'when GraphQL files were changed' do
-      let(:changes_file_content) do
+      let(:changed_files_content) do
         [
           "#{foss_folder}/my_graphql_file.rb",
           "#{foss_folder}/my_other_graphql_file.rb",
@@ -135,7 +137,7 @@ RSpec.describe Tooling::Mappings::GraphqlBaseTypeMappings, feature_category: :to
     end
 
     context 'when files are deleted' do
-      let(:changes_file_content) { "#{foss_folder}/deleted.rb" }
+      let(:changed_files_content) { "#{foss_folder}/deleted.rb" }
 
       it 'returns an empty array' do
         expect(subject).to match_array([])
diff --git a/spec/tooling/lib/tooling/mappings/js_to_system_specs_mappings_spec.rb b/spec/tooling/lib/tooling/mappings/js_to_system_specs_mappings_spec.rb
index c36d14cd267..e1f35bedebb 100644
--- a/spec/tooling/lib/tooling/mappings/js_to_system_specs_mappings_spec.rb
+++ b/spec/tooling/lib/tooling/mappings/js_to_system_specs_mappings_spec.rb
@@ -6,23 +6,25 @@ require_relative '../../../../../tooling/lib/tooling/mappings/js_to_system_specs
 RSpec.describe Tooling::Mappings::JsToSystemSpecsMappings, feature_category: :tooling do
   # We set temporary folders, and those readers give access to those folder paths
   attr_accessor :js_base_folder, :system_specs_base_folder
-  attr_accessor :changes_file, :matching_tests_paths
+  attr_accessor :changed_files_file, :predictive_tests_file
+
+  let(:changed_files_pathname)        { changed_files_file.path    }
+  let(:predictive_tests_pathname)     { predictive_tests_file.path }
+  let(:changed_files_content)         { "changed_file1 changed_file2" }
+  let(:predictive_tests_content) { "previously_matching_spec.rb" }
 
   let(:instance) do
     described_class.new(
-      changes_file,
-      matching_tests_paths,
+      changed_files_pathname,
+      predictive_tests_pathname,
       system_specs_base_folder: system_specs_base_folder,
       js_base_folder: js_base_folder
     )
   end
 
-  let(:changes_file_content)         { "changed_file1 changed_file2" }
-  let(:matching_tests_paths_content) { "previously_matching_spec.rb" }
-
   around do |example|
-    self.changes_file         = Tempfile.new('changes')
-    self.matching_tests_paths = Tempfile.new('matching_tests')
+    self.changed_files_file    = Tempfile.new('changed_files_file')
+    self.predictive_tests_file = Tempfile.new('predictive_tests_file')
 
     Dir.mktmpdir do |tmp_js_base_folder|
       Dir.mktmpdir do |tmp_system_specs_base_folder|
@@ -34,10 +36,10 @@ RSpec.describe Tooling::Mappings::JsToSystemSpecsMappings, feature_category: :to
         begin
           example.run
         ensure
-          changes_file.close
-          matching_tests_paths.close
-          changes_file.unlink
-          matching_tests_paths.unlink
+          changed_files_file.close
+          predictive_tests_file.close
+          changed_files_file.unlink
+          predictive_tests_file.unlink
         end
       end
     end
@@ -45,22 +47,22 @@ RSpec.describe Tooling::Mappings::JsToSystemSpecsMappings, feature_category: :to
 
   before do
     # We write into the temp files initially, to later check how the code modified those files
-    File.write(changes_file, changes_file_content)
-    File.write(matching_tests_paths, matching_tests_paths_content)
+    File.write(changed_files_pathname, changed_files_content)
+    File.write(predictive_tests_pathname, predictive_tests_content)
   end
 
   describe '#execute' do
     subject { instance.execute }
 
     before do
-      File.write(changes_file, changed_files.join(' '))
+      File.write(changed_files_pathname, changed_files.join(' '))
     end
 
     context 'when no JS files were changed' do
       let(:changed_files) { [] }
 
       it 'does not change the output file' do
-        expect { subject }.not_to change { File.read(matching_tests_paths) }
+        expect { subject }.not_to change { File.read(predictive_tests_pathname) }
       end
     end
 
@@ -69,7 +71,7 @@ RSpec.describe Tooling::Mappings::JsToSystemSpecsMappings, feature_category: :to
 
       context 'when the JS files are not present on disk' do
         it 'does not change the output file' do
-          expect { subject }.not_to change { File.read(matching_tests_paths) }
+          expect { subject }.not_to change { File.read(predictive_tests_pathname) }
         end
       end
 
@@ -81,7 +83,7 @@ RSpec.describe Tooling::Mappings::JsToSystemSpecsMappings, feature_category: :to
 
         context 'when no system specs match the JS keyword' do
           it 'does not change the output file' do
-            expect { subject }.not_to change { File.read(matching_tests_paths) }
+            expect { subject }.not_to change { File.read(predictive_tests_pathname) }
           end
         end
 
@@ -92,9 +94,9 @@ RSpec.describe Tooling::Mappings::JsToSystemSpecsMappings, feature_category: :to
           end
 
           it 'adds the new specs to the output file' do
-            expect { subject }.to change { File.read(matching_tests_paths) }
-              .from(matching_tests_paths_content)
-              .to("#{matching_tests_paths_content} #{system_specs_base_folder}/confidential_issues/issues_spec.rb")
+            expect { subject }.to change { File.read(predictive_tests_pathname) }
+              .from(predictive_tests_content)
+              .to("#{predictive_tests_content} #{system_specs_base_folder}/confidential_issues/issues_spec.rb")
           end
         end
       end
@@ -108,7 +110,7 @@ RSpec.describe Tooling::Mappings::JsToSystemSpecsMappings, feature_category: :to
       File.write("#{js_base_folder}/index.js", "index.js")
       File.write("#{js_base_folder}/index-with-ee-in-it.js", "index-with-ee-in-it.js")
       File.write("#{js_base_folder}/index-with-jh-in-it.js", "index-with-jh-in-it.js")
-      File.write(changes_file, changed_files.join(' '))
+      File.write(changed_files_pathname, changed_files.join(' '))
     end
 
     context 'when no files were changed' do
@@ -148,7 +150,7 @@ RSpec.describe Tooling::Mappings::JsToSystemSpecsMappings, feature_category: :to
   end
 
   describe '#construct_js_keywords' do
-    subject { described_class.new(changes_file, matching_tests_paths).construct_js_keywords(js_files) }
+    subject { described_class.new(changed_files_file, predictive_tests_file).construct_js_keywords(js_files) }
 
     let(:js_files) do
       %w[
diff --git a/spec/tooling/lib/tooling/mappings/partial_to_views_mappings_spec.rb b/spec/tooling/lib/tooling/mappings/partial_to_views_mappings_spec.rb
index 30965ed985d..75ddee18985 100644
--- a/spec/tooling/lib/tooling/mappings/partial_to_views_mappings_spec.rb
+++ b/spec/tooling/lib/tooling/mappings/partial_to_views_mappings_spec.rb
@@ -5,15 +5,20 @@ require 'fileutils'
 require_relative '../../../../../tooling/lib/tooling/mappings/partial_to_views_mappings'
 
 RSpec.describe Tooling::Mappings::PartialToViewsMappings, feature_category: :tooling do
-  attr_accessor :view_base_folder, :changes_file, :output_file
+  attr_accessor :view_base_folder, :changed_files_file, :views_with_partials_file
 
-  let(:instance)             { described_class.new(changes_file, output_file, view_base_folder: view_base_folder) }
-  let(:changes_file_content) { "changed_file1 changed_file2" }
-  let(:output_file_content)  { "previously_added_view.html.haml" }
+  let(:instance) do
+    described_class.new(changed_files_pathname, views_with_partials_pathname, view_base_folder: view_base_folder)
+  end
+
+  let(:changed_files_pathname)       { changed_files_file.path }
+  let(:views_with_partials_pathname) { views_with_partials_file.path }
+  let(:changed_files_content)        { "changed_file1 changed_file2" }
+  let(:views_with_partials_content)  { "previously_added_view.html.haml" }
 
   around do |example|
-    self.changes_file        = Tempfile.new('changes')
-    self.output_file         = Tempfile.new('output_file')
+    self.changed_files_file       = Tempfile.new('changed_files_file')
+    self.views_with_partials_file = Tempfile.new('views_with_partials_file')
 
     # See https://ruby-doc.org/stdlib-1.9.3/libdoc/tempfile/rdoc/
     #     Tempfile.html#class-Tempfile-label-Explicit+close
@@ -23,24 +28,24 @@ RSpec.describe Tooling::Mappings::PartialToViewsMappings, feature_category: :too
         example.run
       end
     ensure
-      changes_file.close
-      output_file.close
-      changes_file.unlink
-      output_file.unlink
+      changed_files_file.close
+      views_with_partials_file.close
+      changed_files_file.unlink
+      views_with_partials_file.unlink
     end
   end
 
   before do
     # We write into the temp files initially, to check how the code modified those files
-    File.write(changes_file, changes_file_content)
-    File.write(output_file, output_file_content)
+    File.write(changed_files_pathname, changed_files_content)
+    File.write(views_with_partials_pathname, views_with_partials_content)
   end
 
   describe '#execute' do
     subject { instance.execute }
 
-    let(:changed_files)        { ["#{view_base_folder}/my_view.html.haml"] }
-    let(:changes_file_content) { changed_files.join(" ") }
+    let(:changed_files)         { ["#{view_base_folder}/my_view.html.haml"] }
+    let(:changed_files_content) { changed_files.join(" ") }
 
     before do
       # We create all of the changed_files, so that they are part of the filtered files
@@ -48,12 +53,12 @@ RSpec.describe Tooling::Mappings::PartialToViewsMappings, feature_category: :too
     end
 
     it 'does not modify the content of the input file' do
-      expect { subject }.not_to change { File.read(changes_file) }
+      expect { subject }.not_to change { File.read(changed_files_pathname) }
     end
 
     context 'when no partials were modified' do
       it 'does not change the output file' do
-        expect { subject }.not_to change { File.read(output_file) }
+        expect { subject }.not_to change { File.read(views_with_partials_pathname) }
       end
     end
 
@@ -77,7 +82,7 @@ RSpec.describe Tooling::Mappings::PartialToViewsMappings, feature_category: :too
         end
 
         it 'does not change the output file' do
-          expect { subject }.not_to change { File.read(output_file) }
+          expect { subject }.not_to change { File.read(views_with_partials_pathname) }
         end
       end
 
@@ -87,9 +92,9 @@ RSpec.describe Tooling::Mappings::PartialToViewsMappings, feature_category: :too
         end
 
         it 'writes the view including the partial to the output' do
-          expect { subject }.to change { File.read(output_file) }
-                            .from(output_file_content)
-                            .to(output_file_content + " #{view_base_folder}/my_view.html.haml")
+          expect { subject }.to change { File.read(views_with_partials_pathname) }
+                            .from(views_with_partials_content)
+                            .to(views_with_partials_content + " #{view_base_folder}/my_view.html.haml")
         end
       end
     end
@@ -98,7 +103,7 @@ RSpec.describe Tooling::Mappings::PartialToViewsMappings, feature_category: :too
   describe '#filter_files' do
     subject { instance.filter_files }
 
-    let(:changes_file_content) { file_path }
+    let(:changed_files_content) { file_path }
 
     context 'when the file does not exist on disk' do
       let(:file_path) { "#{view_base_folder}/_index.html.erb" }
@@ -164,11 +169,11 @@ RSpec.describe Tooling::Mappings::PartialToViewsMappings, feature_category: :too
 
       before do
         FileUtils.mkdir_p("#{view_base_folder}/components/subfolder")
-        File.write(changes_file_content, "I am a partial!")
+        File.write(changed_files_content, "I am a partial!")
       end
 
       context 'when the partial is not part of the changed files' do
-        let(:changes_file_content) { "#{view_base_folder}/components/subfolder/_not_the_partial.html.haml" }
+        let(:changed_files_content) { "#{view_base_folder}/components/subfolder/_not_the_partial.html.haml" }
 
         it 'returns false' do
           expect(subject).to be_falsey
@@ -176,7 +181,7 @@ RSpec.describe Tooling::Mappings::PartialToViewsMappings, feature_category: :too
       end
 
       context 'when the partial is part of the changed files' do
-        let(:changes_file_content) { "#{view_base_folder}/components/subfolder/_relative_partial.html.haml" }
+        let(:changed_files_content) { "#{view_base_folder}/components/subfolder/_relative_partial.html.haml" }
 
         it 'returns true' do
           expect(subject).to be_truthy
@@ -191,11 +196,11 @@ RSpec.describe Tooling::Mappings::PartialToViewsMappings, feature_category: :too
       before do
         FileUtils.mkdir_p("#{view_base_folder}/components")
         FileUtils.mkdir_p("#{view_base_folder}/shared")
-        File.write(changes_file_content, "I am a partial!")
+        File.write(changed_files_content, "I am a partial!")
       end
 
       context 'when the partial is not part of the changed files' do
-        let(:changes_file_content) { "#{view_base_folder}/shared/not_the_partial" }
+        let(:changed_files_content) { "#{view_base_folder}/shared/not_the_partial" }
 
         it 'returns false' do
           expect(subject).to be_falsey
@@ -203,7 +208,7 @@ RSpec.describe Tooling::Mappings::PartialToViewsMappings, feature_category: :too
       end
 
       context 'when the partial is part of the changed files' do
-        let(:changes_file_content) { "#{view_base_folder}/shared/_absolute_partial.html.haml" }
+        let(:changed_files_content) { "#{view_base_folder}/shared/_absolute_partial.html.haml" }
 
         it 'returns true' do
           expect(subject).to be_truthy
diff --git a/spec/tooling/lib/tooling/mappings/view_to_js_mappings_spec.rb b/spec/tooling/lib/tooling/mappings/view_to_js_mappings_spec.rb
index bf07ad1951b..6d007843716 100644
--- a/spec/tooling/lib/tooling/mappings/view_to_js_mappings_spec.rb
+++ b/spec/tooling/lib/tooling/mappings/view_to_js_mappings_spec.rb
@@ -6,23 +6,25 @@ require_relative '../../../../../tooling/lib/tooling/mappings/view_to_js_mapping
 RSpec.describe Tooling::Mappings::ViewToJsMappings, feature_category: :tooling do
   # We set temporary folders, and those readers give access to those folder paths
   attr_accessor :view_base_folder, :js_base_folder
-  attr_accessor :changes_file, :matching_tests_paths
+  attr_accessor :changed_files_file, :predictive_tests_file
+
+  let(:changed_files_pathname)    { changed_files_file.path }
+  let(:predictive_tests_pathname) { predictive_tests_file.path }
+  let(:changed_files_content)     { "changed_file1 changed_file2" }
+  let(:predictive_tests_content)  { "previously_matching_spec.rb" }
 
   let(:instance) do
     described_class.new(
-      changes_file,
-      matching_tests_paths,
+      changed_files_pathname,
+      predictive_tests_pathname,
       view_base_folder: view_base_folder,
       js_base_folder: js_base_folder
     )
   end
 
-  let(:changes_file_content)         { "changed_file1 changed_file2" }
-  let(:matching_tests_paths_content) { "previously_matching_spec.rb" }
-
   around do |example|
-    self.changes_file         = Tempfile.new('changes')
-    self.matching_tests_paths = Tempfile.new('matching_tests')
+    self.changed_files_file = Tempfile.new('changed_files_file')
+    self.predictive_tests_file = Tempfile.new('matching_tests')
 
     Dir.mktmpdir do |tmp_js_base_folder|
       Dir.mktmpdir do |tmp_views_base_folder|
@@ -34,10 +36,10 @@ RSpec.describe Tooling::Mappings::ViewToJsMappings, feature_category: :tooling d
         begin
           example.run
         ensure
-          changes_file.close
-          matching_tests_paths.close
-          changes_file.unlink
-          matching_tests_paths.unlink
+          changed_files_file.close
+          predictive_tests_file.close
+          changed_files_file.unlink
+          predictive_tests_file.unlink
         end
       end
     end
@@ -45,8 +47,8 @@ RSpec.describe Tooling::Mappings::ViewToJsMappings, feature_category: :tooling d
 
   before do
     # We write into the temp files initially, to later check how the code modified those files
-    File.write(changes_file, changes_file_content)
-    File.write(matching_tests_paths, matching_tests_paths_content)
+    File.write(changed_files_pathname, changed_files_content)
+    File.write(predictive_tests_pathname, predictive_tests_content)
   end
 
   describe '#execute' do
@@ -55,7 +57,7 @@ RSpec.describe Tooling::Mappings::ViewToJsMappings, feature_category: :tooling d
     subject { instance.execute }
 
     before do
-      File.write(changes_file, changed_files.join(' '))
+      File.write(changed_files_pathname, changed_files.join(' '))
     end
 
     context 'when no view files have been changed' do
@@ -64,7 +66,7 @@ RSpec.describe Tooling::Mappings::ViewToJsMappings, feature_category: :tooling d
       end
 
       it 'does not change the output file' do
-        expect { subject }.not_to change { File.read(matching_tests_paths) }
+        expect { subject }.not_to change { File.read(predictive_tests_pathname) }
       end
     end
 
@@ -82,7 +84,7 @@ RSpec.describe Tooling::Mappings::ViewToJsMappings, feature_category: :tooling d
         end
 
         it 'does not change the output file' do
-          expect { subject }.not_to change { File.read(matching_tests_paths) }
+          expect { subject }.not_to change { File.read(predictive_tests_pathname) }
         end
       end
 
@@ -99,7 +101,7 @@ RSpec.describe Tooling::Mappings::ViewToJsMappings, feature_category: :tooling d
 
         context 'when no matching JS files are found' do
           it 'does not change the output file' do
-            expect { subject }.not_to change { File.read(matching_tests_paths) }
+            expect { subject }.not_to change { File.read(predictive_tests_pathname) }
           end
         end
 
@@ -119,9 +121,9 @@ RSpec.describe Tooling::Mappings::ViewToJsMappings, feature_category: :tooling d
           end
 
           it 'adds the matching JS files to the output' do
-            expect { subject }.to change { File.read(matching_tests_paths) }
-              .from(matching_tests_paths_content)
-              .to("#{matching_tests_paths_content} #{js_base_folder}/index.js")
+            expect { subject }.to change { File.read(predictive_tests_pathname) }
+              .from(predictive_tests_content)
+              .to("#{predictive_tests_content} #{js_base_folder}/index.js")
           end
         end
       end
@@ -165,9 +167,9 @@ RSpec.describe Tooling::Mappings::ViewToJsMappings, feature_category: :tooling d
       end
 
       it 'scans those partials for the HTML attribute value' do
-        expect { subject }.to change { File.read(matching_tests_paths) }
-        .from(matching_tests_paths_content)
-        .to("#{matching_tests_paths_content} #{js_base_folder}/index.js")
+        expect { subject }.to change { File.read(predictive_tests_pathname) }
+        .from(predictive_tests_content)
+        .to("#{predictive_tests_content} #{js_base_folder}/index.js")
       end
     end
   end
@@ -178,7 +180,7 @@ RSpec.describe Tooling::Mappings::ViewToJsMappings, feature_category: :tooling d
     before do
       File.write("#{js_base_folder}/index.js", "index.js")
       File.write("#{view_base_folder}/index.html", "index.html")
-      File.write(changes_file, changed_files.join(' '))
+      File.write(changed_files_pathname, changed_files.join(' '))
     end
 
     context 'when no files were changed' do
diff --git a/spec/tooling/lib/tooling/mappings/view_to_system_specs_mappings_spec.rb b/spec/tooling/lib/tooling/mappings/view_to_system_specs_mappings_spec.rb
index d4f4bbd7f06..b8a13c50c9b 100644
--- a/spec/tooling/lib/tooling/mappings/view_to_system_specs_mappings_spec.rb
+++ b/spec/tooling/lib/tooling/mappings/view_to_system_specs_mappings_spec.rb
@@ -5,15 +5,20 @@ require 'fileutils'
 require_relative '../../../../../tooling/lib/tooling/mappings/view_to_system_specs_mappings'
 
 RSpec.describe Tooling::Mappings::ViewToSystemSpecsMappings, feature_category: :tooling do
-  attr_accessor :view_base_folder, :changes_file, :output_file
+  attr_accessor :view_base_folder, :changed_files_file, :predictive_tests_file
 
-  let(:instance) { described_class.new(changes_file, output_file, view_base_folder: view_base_folder) }
-  let(:changes_file_content)        { "changed_file1 changed_file2" }
-  let(:output_file_initial_content) { "previously_added_spec.rb" }
+  let(:instance) do
+    described_class.new(changed_files_pathname, predictive_tests_pathname, view_base_folder: view_base_folder)
+  end
+
+  let(:changed_files_pathname)           { changed_files_file.path }
+  let(:predictive_tests_pathname)        { predictive_tests_file.path }
+  let(:changed_files_content)            { "changed_file1 changed_file2" }
+  let(:predictive_tests_initial_content) { "previously_added_spec.rb" }
 
   around do |example|
-    self.changes_file        = Tempfile.new('changes')
-    self.output_file         = Tempfile.new('output_file')
+    self.changed_files_file    = Tempfile.new('changed_files_file')
+    self.predictive_tests_file = Tempfile.new('predictive_tests_file')
 
     # See https://ruby-doc.org/stdlib-1.9.3/libdoc/tempfile/rdoc/
     #     Tempfile.html#class-Tempfile-label-Explicit+close
@@ -23,10 +28,10 @@ RSpec.describe Tooling::Mappings::ViewToSystemSpecsMappings, feature_category: :
         example.run
       end
     ensure
-      changes_file.close
-      output_file.close
-      changes_file.unlink
-      output_file.unlink
+      changed_files_file.close
+      predictive_tests_file.close
+      changed_files_file.unlink
+      predictive_tests_file.unlink
     end
   end
 
@@ -34,13 +39,13 @@ RSpec.describe Tooling::Mappings::ViewToSystemSpecsMappings, feature_category: :
     FileUtils.mkdir_p("#{view_base_folder}/app/views/dashboard")
 
     # We write into the temp files initially, to check how the code modified those files
-    File.write(changes_file, changes_file_content)
-    File.write(output_file, output_file_initial_content)
+    File.write(changed_files_pathname, changed_files_content)
+    File.write(predictive_tests_pathname, predictive_tests_initial_content)
   end
 
   shared_examples 'writes nothing to the output file' do
     it 'writes nothing to the output file' do
-      expect { subject }.not_to change { File.read(changes_file) }
+      expect { subject }.not_to change { File.read(changed_files_pathname) }
     end
   end
 
@@ -48,7 +53,7 @@ RSpec.describe Tooling::Mappings::ViewToSystemSpecsMappings, feature_category: :
     subject { instance.execute }
 
     let(:changed_files)        { ["#{view_base_folder}/app/views/dashboard/my_view.html.haml"] }
-    let(:changes_file_content) { changed_files.join(" ") }
+    let(:changed_files_content) { changed_files.join(" ") }
 
     before do
       # We create all of the changed_files, so that they are part of the filtered files
@@ -88,9 +93,9 @@ RSpec.describe Tooling::Mappings::ViewToSystemSpecsMappings, feature_category: :
           end
 
           it 'writes that feature spec to the output file' do
-            expect { subject }.to change { File.read(output_file) }
-                              .from(output_file_initial_content)
-                              .to("#{output_file_initial_content} #{expected_feature_spec}")
+            expect { subject }.to change { File.read(predictive_tests_pathname) }
+                              .from(predictive_tests_initial_content)
+                              .to("#{predictive_tests_initial_content} #{expected_feature_spec}")
           end
         end
 
@@ -111,9 +116,9 @@ RSpec.describe Tooling::Mappings::ViewToSystemSpecsMappings, feature_category: :
           end
 
           it 'writes all of the feature specs for the parent folder to the output file' do
-            expect { subject }.to change { File.read(output_file) }
-                              .from(output_file_initial_content)
-                              .to("#{output_file_initial_content} #{expected_feature_specs.join(' ')}")
+            expect { subject }.to change { File.read(predictive_tests_pathname) }
+                              .from(predictive_tests_initial_content)
+                              .to("#{predictive_tests_initial_content} #{expected_feature_specs.join(' ')}")
           end
         end
       end
diff --git a/spec/tooling/lib/tooling/predictive_tests_spec.rb b/spec/tooling/lib/tooling/predictive_tests_spec.rb
new file mode 100644
index 00000000000..79554037c48
--- /dev/null
+++ b/spec/tooling/lib/tooling/predictive_tests_spec.rb
@@ -0,0 +1,109 @@
+# frozen_string_literal: true
+
+require 'tempfile'
+require_relative '../../../../tooling/lib/tooling/predictive_tests'
+require_relative '../../../support/helpers/stub_env'
+
+RSpec.describe Tooling::PredictiveTests, feature_category: :tooling do
+  include StubENV
+
+  let(:instance)                       { described_class.new }
+  let(:matching_tests_initial_content) { 'initial_matching_spec' }
+
+  attr_accessor :changed_files, :fixtures_mapping, :matching_js_files, :matching_tests, :views_with_partials
+
+  around do |example|
+    self.changed_files       = Tempfile.new('test-folder/changed_files.txt')
+    self.fixtures_mapping    = Tempfile.new('test-folder/fixtures_mapping.txt')
+    self.matching_js_files   = Tempfile.new('test-folder/matching_js_files.txt')
+    self.matching_tests      = Tempfile.new('test-folder/matching_tests.txt')
+    self.views_with_partials = Tempfile.new('test-folder/views_with_partials.txt')
+
+    # See https://ruby-doc.org/stdlib-1.9.3/libdoc/tempfile/rdoc/
+    #     Tempfile.html#class-Tempfile-label-Explicit+close
+    begin
+      example.run
+    ensure
+      changed_files.close
+      changed_files.unlink
+      fixtures_mapping.close
+      fixtures_mapping.unlink
+      matching_js_files.close
+      matching_js_files.unlink
+      matching_tests.close
+      matching_tests.unlink
+      views_with_partials.close
+      views_with_partials.unlink
+    end
+  end
+
+  before do
+    stub_env(
+      'RSPEC_CHANGED_FILES_PATH' => changed_files.path,
+      'RSPEC_MATCHING_TESTS_PATH' => matching_tests.path,
+      'RSPEC_VIEWS_INCLUDING_PARTIALS_PATH' => views_with_partials.path,
+      'FRONTEND_FIXTURES_MAPPING_PATH' => fixtures_mapping.path,
+      'RSPEC_MATCHING_JS_FILES_PATH' => matching_js_files.path,
+      'RSPEC_TESTS_MAPPING_ENABLED' => "false",
+      'RSPEC_TESTS_MAPPING_PATH' => '/tmp/does-not-exist.out'
+    )
+
+    # We write some data to later on verify that we only append to this file.
+    File.write(matching_tests.path, matching_tests_initial_content)
+    File.write(fixtures_mapping.path, '{}') # We write valid JSON, so that the file can be processed
+  end
+
+  describe '#execute' do
+    subject { instance.execute }
+
+    context 'when ENV variables are missing' do
+      before do
+        stub_env(
+          'RSPEC_CHANGED_FILES_PATH' => '',
+          'FRONTEND_FIXTURES_MAPPING_PATH' => ''
+        )
+      end
+
+      it 'raises an error' do
+        expect { subject }.to raise_error(
+          '[predictive tests] Missing ENV variable(s): RSPEC_CHANGED_FILES_PATH,FRONTEND_FIXTURES_MAPPING_PATH.'
+        )
+      end
+    end
+
+    context 'when all ENV variables are provided' do
+      before do
+        File.write(changed_files, changed_files_content)
+      end
+
+      context 'when no files were changed' do
+        let(:changed_files_content) { '' }
+
+        it 'does not change any files' do
+          expect { subject }.not_to change { File.read(changed_files.path) }
+          expect { subject }.not_to change { File.read(matching_tests.path) }
+          expect { subject }.not_to change { File.read(views_with_partials.path) }
+          expect { subject }.not_to change { File.read(fixtures_mapping.path) }
+          expect { subject }.not_to change { File.read(matching_js_files.path) }
+        end
+      end
+
+      context 'when some files were changed' do
+        let(:changed_files_content) { 'tooling/lib/tooling/predictive_tests.rb' }
+
+        it 'appends the spec file to RSPEC_MATCHING_TESTS_PATH' do
+          expect { subject }.to change { File.read(matching_tests.path) }
+            .from(matching_tests_initial_content)
+            .to("#{matching_tests_initial_content} spec/tooling/lib/tooling/predictive_tests_spec.rb")
+        end
+
+        it 'does not change files other than RSPEC_MATCHING_TESTS_PATH' do
+          expect { subject }.not_to change { File.read(changed_files.path) }
+          expect { subject }.not_to change { File.read(views_with_partials.path) }
+          expect { subject }.not_to change { File.read(fixtures_mapping.path) }
+          expect { subject }.not_to change { File.read(matching_js_files.path) }
+        end
+      end
+    end
+  end
+end