Change test runner on --fail-fast to report first error deterministic…

…ally

Changelog.md

@@ -1,3 +1,11 @@
+# v0.12.1 2024-05-11
+
+* [#1443](https://github.com/mbj/mutant/pull/1443)
+
+  In regular single threaded test execution (Rspec native) `--fail-fast` stops at the first error. Mutants
+  rspec/minitest execution option can reach multiple errors on parallel execution before the parallel engine can
+  react to the first known error. This change makes sure only the first error gets reported when using `--fail-fast`.
+
 # v0.12.0 2024-04-22
 
   Drop the license gem, entirely. This reduces DRM in mutants code base to the absolute minimum.

lib/mutant/reporter/cli/printer/test.rb

@@ -68,7 +68,7 @@ class EnvResult < self
             #
             # @return [undefined]
             def run
-              visit_collection(Result, object.failed_test_results)
+              visit_failed
               visit(Env, object.env)
               FORMATS.each do |report, format, value|
                 __send__(report, format, __send__(value))
@@ -77,6 +77,27 @@ def run
 
           private
 
+            def visit_failed
+              failed = object.failed_test_results
+
+              if object.env.config.fail_fast
+                visit_failed_tests(failed.take(1))
+                visit_other_failed(failed.drop(1))
+              else
+                visit_failed_tests(failed)
+              end
+            end
+
+            def visit_other_failed(other)
+              return if other.empty?
+
+              puts('Other failed tests (report suppressed from fail fast): %d' % other.length)
+            end
+
+            def visit_failed_tests(failed)
+              visit_collection(Result, failed)
+            end
+
             def efficiency_percent
               (testtime / runtime) * 100
             end

spec/unit/mutant/reporter/cli/printer/test/env_result_spec.rb

@@ -13,34 +13,99 @@
 
   let(:test_result_a) do
     Mutant::Result::Test.new(
-      output:  '<test-output>',
+      output:  '<test-output-a>',
       passed:  false,
       runtime: 0.1
     )
   end
 
   let(:test_result_b) do
     Mutant::Result::Test.new(
-      output:  '<test-output>',
+      output:  '<test-output-b>',
       passed:  true,
       runtime: 0.2
     )
   end
 
   describe '.call' do
-    it_reports <<~'STR'
-      <test-output>
-      Test environment:
-      Fail-Fast:    false
-      Integration:  null
-      Jobs:         auto
-      Tests:        2
-      Test-Results: 2
-      Test-Failed:  1
-      Test-Success: 1
-      Runtime:      0.80s
-      Testtime:     0.30s
-      Efficiency:   37.50%
-    STR
+    context 'single test failure' do
+      context 'without fail fast' do
+        it_reports <<~'STR'
+          <test-output-a>
+          Test environment:
+          Fail-Fast:    false
+          Integration:  null
+          Jobs:         auto
+          Tests:        2
+          Test-Results: 2
+          Test-Failed:  1
+          Test-Success: 1
+          Runtime:      0.80s
+          Testtime:     0.30s
+          Efficiency:   37.50%
+        STR
+      end
+
+      context 'with fail fast' do
+        let(:config) { super().with(fail_fast: true) }
+
+        it_reports <<~'STR'
+          <test-output-a>
+          Test environment:
+          Fail-Fast:    true
+          Integration:  null
+          Jobs:         auto
+          Tests:        2
+          Test-Results: 2
+          Test-Failed:  1
+          Test-Success: 1
+          Runtime:      0.80s
+          Testtime:     0.30s
+          Efficiency:   37.50%
+        STR
+      end
+    end
+
+    context 'with multiple test failures' do
+      let(:test_result_b) { super().with(passed: false) }
+
+      context 'without fail fast' do
+        it_reports <<~'STR'
+          <test-output-a>
+          <test-output-b>
+          Test environment:
+          Fail-Fast:    false
+          Integration:  null
+          Jobs:         auto
+          Tests:        2
+          Test-Results: 2
+          Test-Failed:  2
+          Test-Success: 0
+          Runtime:      0.80s
+          Testtime:     0.30s
+          Efficiency:   37.50%
+        STR
+      end
+
+      context 'with fail fast' do
+        let(:config) { super().with(fail_fast: true) }
+
+        it_reports <<~'STR'
+          <test-output-a>
+          Other failed tests (report suppressed from fail fast): 1
+          Test environment:
+          Fail-Fast:    true
+          Integration:  null
+          Jobs:         auto
+          Tests:        2
+          Test-Results: 2
+          Test-Failed:  2
+          Test-Success: 0
+          Runtime:      0.80s
+          Testtime:     0.30s
+          Efficiency:   37.50%
+        STR
+      end
+    end
   end
 end