1 files changed, 134 insertions, 0 deletions
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..b82364fe6f6
--- /dev/null
+++ b/spec/tooling/lib/tooling/predictive_tests_spec.rb
@@ -0,0 +1,134 @@
+# frozen_string_literal: true
+
+require 'tempfile'
+require 'fileutils'
+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' }
+  let(:fixtures_mapping_content)       { '{}' }
+
+  attr_accessor :changed_files, :changed_files_path, :fixtures_mapping,
+    :matching_js_files, :matching_tests, :views_with_partials
+
+  around do |example|
+    self.changed_files       = Tempfile.new('test-folder/changed_files.txt')
+    self.changed_files_path  = changed_files.path
+    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
+      # In practice, we let PredictiveTests create the file, and we just
+      # use its file name.
+      changed_files.close
+      changed_files.unlink
+
+      example.run
+    ensure
+      # Since example.run can create the file again, let's remove it again
+      FileUtils.rm_f(changed_files_path)
+      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, fixtures_mapping_content)
+
+    allow(Gitlab).to receive(:configure)
+  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
+        change = double('GitLab::Change') # rubocop:disable RSpec/VerifiedDoubles
+        allow(change).to receive_message_chain(:to_h, :values_at)
+          .and_return([changed_files_content, changed_files_content])
+
+        allow(Gitlab).to receive_message_chain(:merge_request_changes, :changes)
+          .and_return([change])
+      end
+
+      context 'when no files were changed' do
+        let(:changed_files_content) { '' }
+
+        it 'does not change files other than RSPEC_CHANGED_FILES_PATH' do
+          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 used for frontend fixtures were changed' do
+        let(:changed_files_content) { 'app/models/todo.rb' }
+        let(:changed_files_matching_test) { 'spec/models/todo_spec.rb' }
+        let(:matching_frontend_fixture) { 'tmp/tests/frontend/fixtures-ee/todos/todos.html' }
+        let(:fixtures_mapping_content) do
+          JSON.dump(changed_files_matching_test => [matching_frontend_fixture]) # rubocop:disable Gitlab/Json
+        end
+
+        it 'writes to RSPEC_CHANGED_FILES_PATH with API contents and appends with matching fixtures' do
+          subject
+
+          expect(File.read(changed_files_path)).to eq("#{changed_files_content} #{matching_frontend_fixture}")
+        end
+
+        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} #{changed_files_matching_test}")
+        end
+
+        it 'does not change files other than RSPEC_CHANGED_FILES_PATH nor RSPEC_MATCHING_TESTS_PATH' do
+          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