1 files changed, 84 insertions, 0 deletions
diff --git a/spec/lib/gitlab/diff/pair_selector_spec.rb b/spec/lib/gitlab/diff/pair_selector_spec.rb
new file mode 100644
index 00000000000..da5707bc377
--- /dev/null
+++ b/spec/lib/gitlab/diff/pair_selector_spec.rb
@@ -0,0 +1,84 @@
+# frozen_string_literal: true
+
+require 'fast_spec_helper'
+
+RSpec.describe Gitlab::Diff::PairSelector do
+  subject(:selector) { described_class.new(lines) }
+
+  describe '#to_a' do
+    subject { selector.to_a }
+
+    let(:lines) { diff.lines }
+
+    let(:diff) do
+      <<-EOF.strip_heredoc
+         class Test                       # 0
+        -  def initialize(test = true)    # 1
+        +  def initialize(test = false)   # 2
+             @test = test                 # 3
+        -    if true                      # 4
+        -      @foo = "bar"               # 5
+        +    unless false                 # 6
+        +      @foo = "baz"               # 7
+             end
+           end
+         end
+      EOF
+    end
+
+    it 'finds all pairs' do
+      is_expected.to match_array([[1, 2], [4, 6], [5, 7]])
+    end
+
+    context 'when there are empty lines' do
+      let(:lines) { ['- bar', '+ baz', ''] }
+
+      it { expect { subject }.not_to raise_error }
+    end
+
+    context 'when there are only removals' do
+      let(:diff) do
+        <<-EOF.strip_heredoc
+          - class Test
+          -  def initialize(test = true)
+          -  end
+          - end
+        EOF
+      end
+
+      it 'returns empty collection' do
+        is_expected.to eq([])
+      end
+    end
+
+    context 'when there are only additions' do
+      let(:diff) do
+        <<-EOF.strip_heredoc
+          + class Test
+          +  def initialize(test = true)
+          +  end
+          + end
+        EOF
+      end
+
+      it 'returns empty collection' do
+        is_expected.to eq([])
+      end
+    end
+
+    context 'when there are no changes' do
+      let(:diff) do
+        <<-EOF.strip_heredoc
+           class Test
+             def initialize(test = true)
+             end
+           end
+        EOF
+      end
+
+      it 'returns empty collection' do
+        is_expected.to eq([])
+      end
+    end
+  end
+end