1 files changed, 117 insertions, 0 deletions
diff --git a/spec/support/shared_examples/migrations/swap_conversion_columns_shared_examples.rb b/spec/support/shared_examples/migrations/swap_conversion_columns_shared_examples.rb
new file mode 100644
index 00000000000..d333641b764
--- /dev/null
+++ b/spec/support/shared_examples/migrations/swap_conversion_columns_shared_examples.rb
@@ -0,0 +1,117 @@
+# frozen_string_literal: true
+
+COLUMN_OPTIONS_TO_REMAIN =
+  %i[
+    null
+    serial?
+    collation
+    default
+    default_function
+  ].freeze
+
+SQL_TYPE_OPTIONS_TO_REMAIN =
+  %i[
+    precision
+    scale
+  ].freeze
+
+SQL_TYPE_OPTIONS_TO_CHANGE =
+  %i[
+    type
+    sql_type
+    limit
+  ].freeze
+
+RSpec.shared_examples 'swap conversion columns' do |table_name:, from:, to:|
+  it 'correctly swaps conversion columns' do
+    before_from_column = before_to_column = before_indexes = before_foreign_keys = nil
+    after_from_column = after_to_column = after_indexes = after_foreign_keys = nil
+
+    expect_column_type_is_changed_but_others_remain_unchanged = -> do
+      # SQL type is changed
+      SQL_TYPE_OPTIONS_TO_CHANGE.each do |sql_type_option|
+        expect(
+          after_from_column.sql_type_metadata.public_send(sql_type_option)
+        ).to eq(
+          before_to_column.sql_type_metadata.public_send(sql_type_option)
+        )
+
+        expect(
+          after_to_column.sql_type_metadata.public_send(sql_type_option)
+        ).to eq(
+          before_from_column.sql_type_metadata.public_send(sql_type_option)
+        )
+      end
+
+      # column metadata remains unchanged
+      COLUMN_OPTIONS_TO_REMAIN.each do |column_option|
+        expect(
+          after_from_column.public_send(column_option)
+        ).to eq(
+          before_from_column.public_send(column_option)
+        )
+
+        expect(
+          after_to_column.public_send(column_option)
+        ).to eq(
+          before_to_column.public_send(column_option)
+        )
+      end
+
+      SQL_TYPE_OPTIONS_TO_REMAIN.each do |sql_type_option|
+        expect(
+          after_from_column.sql_type_metadata.public_send(sql_type_option)
+        ).to eq(
+          before_from_column.sql_type_metadata.public_send(sql_type_option)
+        )
+
+        expect(
+          after_to_column.sql_type_metadata.public_send(sql_type_option)
+        ).to eq(
+          before_to_column.sql_type_metadata.public_send(sql_type_option)
+        )
+      end
+
+      # indexes remain unchanged
+      expect(before_indexes).to eq(after_indexes)
+
+      # foreign keys remain unchanged
+      expect(before_foreign_keys).to eq(after_foreign_keys)
+    end
+
+    find_column_by = ->(name) do
+      active_record_base.connection.columns(table_name).find { |c| c.name == name.to_s }
+    end
+
+    find_indexes = -> do
+      active_record_base.connection.indexes(table_name)
+    end
+
+    find_foreign_keys = -> do
+      Gitlab::Database::PostgresForeignKey.by_constrained_table_name(table_name)
+    end
+
+    reversible_migration do |migration|
+      migration.before -> {
+        before_from_column = find_column_by.call(from)
+        before_to_column = find_column_by.call(to)
+        before_indexes = find_indexes
+        before_foreign_keys = find_foreign_keys
+
+        next if after_from_column.nil?
+
+        # For migrate down
+        expect_column_type_is_changed_but_others_remain_unchanged.call
+      }
+
+      migration.after -> {
+        after_from_column = find_column_by.call(from)
+        after_to_column = find_column_by.call(to)
+        after_indexes = find_indexes
+        after_foreign_keys = find_foreign_keys
+
+        expect_column_type_is_changed_but_others_remain_unchanged.call
+      }
+    end
+  end
+end