Merge branch '288334-avoid-calculating-testing-files-twice-in-parallel_rspec_runner' into 'master'

Resolve "Avoid calculating testing files twice in parallel_rspec_runner"

See merge request gitlab-org/gitlab!48643

.gitlab/ci/rules.gitlab-ci.yml

@@ -157,6 +157,7 @@
   - "{,ee/}fixtures/**/*"
   - "{,ee/}rubocop/**/*"
   - "{,ee/}spec/**/*"
+  - "{,spec/}tooling/**/*"
 
 .code-patterns: &code-patterns
   - "{package.json,yarn.lock}"
@@ -203,6 +204,7 @@
   - "{,ee/}fixtures/**/*"
   - "{,ee/}rubocop/**/*"
   - "{,ee/}spec/**/*"
+  - "{,spec/}tooling/**/*"
 
 .code-qa-patterns: &code-qa-patterns
   - "{package.json,yarn.lock}"
@@ -248,6 +250,7 @@
   - "{,ee/}fixtures/**/*"
   - "{,ee/}rubocop/**/*"
   - "{,ee/}spec/**/*"
+  - "{,spec/}tooling/**/*"
   # QA changes
   - ".dockerignore"
   - "qa/**/*"

tooling/lib/tooling/parallel_rspec_runner.rb

@@ -11,6 +11,9 @@ require 'knapsack'
 #
 # Only the test files allocated by Knapsack and listed in the file
 # would be executed in the CI node.
+#
+# Reference:
+# https://github.com/ArturT/knapsack/blob/v1.20.0/lib/knapsack/runners/rspec_runner.rb
 module Tooling
   class ParallelRSpecRunner
     def self.run(rspec_args: nil, filter_tests_file: nil)
@@ -54,7 +57,7 @@ module Tooling
     def tests_to_run
       return node_tests if filter_tests.empty?
 
-      node_tests & filter_tests
+      @tests_to_run ||= node_tests & filter_tests
     end
 
     def node_tests
@@ -62,7 +65,8 @@ module Tooling
     end
 
     def filter_tests
-      filter_tests_file ? tests_from_file(filter_tests_file) : []
+      @filter_tests ||=
+        filter_tests_file ? tests_from_file(filter_tests_file) : []
     end
 
     def tests_from_file(filter_tests_file)