1 files changed, 101 insertions, 0 deletions
diff --git a/spec/services/issue_rebalancing_service_spec.rb b/spec/services/issue_rebalancing_service_spec.rb
new file mode 100644
index 00000000000..94f594c8083
--- /dev/null
+++ b/spec/services/issue_rebalancing_service_spec.rb
@@ -0,0 +1,101 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe IssueRebalancingService do
+  let_it_be(:project) { create(:project) }
+  let_it_be(:user) { project.creator }
+  let_it_be(:start) { RelativePositioning::START_POSITION }
+  let_it_be(:max_pos) { RelativePositioning::MAX_POSITION }
+  let_it_be(:min_pos) { RelativePositioning::MIN_POSITION }
+  let_it_be(:clump_size) { 300 }
+
+  let_it_be(:unclumped) do
+    (0..clump_size).to_a.map do |i|
+      create(:issue, project: project, author: user, relative_position: start + (1024 * i))
+    end
+  end
+
+  let_it_be(:end_clump) do
+    (0..clump_size).to_a.map do |i|
+      create(:issue, project: project, author: user, relative_position: max_pos - i)
+    end
+  end
+
+  let_it_be(:start_clump) do
+    (0..clump_size).to_a.map do |i|
+      create(:issue, project: project, author: user, relative_position: min_pos + i)
+    end
+  end
+
+  def issues_in_position_order
+    project.reload.issues.reorder(relative_position: :asc).to_a
+  end
+
+  it 'rebalances a set of issues with clumps at the end and start' do
+    all_issues = start_clump + unclumped + end_clump.reverse
+    service = described_class.new(project.issues.first)
+
+    expect { service.execute }.not_to change { issues_in_position_order.map(&:id) }
+
+    all_issues.each(&:reset)
+
+    gaps = all_issues.take(all_issues.count - 1).zip(all_issues.drop(1)).map do |a, b|
+      b.relative_position - a.relative_position
+    end
+
+    expect(gaps).to all(be > RelativePositioning::MIN_GAP)
+    expect(all_issues.first.relative_position).to be > (RelativePositioning::MIN_POSITION * 0.9999)
+    expect(all_issues.last.relative_position).to be < (RelativePositioning::MAX_POSITION * 0.9999)
+  end
+
+  it 'is idempotent' do
+    service = described_class.new(project.issues.first)
+
+    expect do
+      service.execute
+      service.execute
+    end.not_to change { issues_in_position_order.map(&:id) }
+  end
+
+  it 'does nothing if the feature flag is disabled' do
+    stub_feature_flags(rebalance_issues: false)
+    issue = project.issues.first
+    issue.project
+    issue.project.group
+    old_pos = issue.relative_position
+
+    service = described_class.new(issue)
+
+    expect { service.execute }.not_to exceed_query_limit(0)
+    expect(old_pos).to eq(issue.reload.relative_position)
+  end
+
+  it 'acts if the flag is enabled for the project' do
+    issue = create(:issue, project: project, author: user, relative_position: max_pos)
+    stub_feature_flags(rebalance_issues: issue.project)
+
+    service = described_class.new(issue)
+
+    expect { service.execute }.to change { issue.reload.relative_position }
+  end
+
+  it 'acts if the flag is enabled for the group' do
+    issue = create(:issue, project: project, author: user, relative_position: max_pos)
+    project.update!(group: create(:group))
+    stub_feature_flags(rebalance_issues: issue.project.group)
+
+    service = described_class.new(issue)
+
+    expect { service.execute }.to change { issue.reload.relative_position }
+  end
+
+  it 'aborts if there are too many issues' do
+    issue = project.issues.first
+    base = double(count: 10_001)
+
+    allow(Issue).to receive(:relative_positioning_query_base).with(issue).and_return(base)
+
+    expect { described_class.new(issue).execute }.to raise_error(described_class::TooManyIssues)
+  end
+end