chore: Parallelize mutating projects and running the initial test

[richardwerkman]

I'm expecting a modest performance improvement from this on large projects. After this change we:

• Run the initial test while mutating the syntax trees
• Mutate syntax trees in parallel, instead of mutate projects in parallel

This will use up more threads, but reduces the runtime of stryker on multi core systems.

Test results:
I got the initial testing and mutating duration on the integration test project down from 4500ms to 1600ms on a 10 core system.

todo:

• Test on a real world project to measure performance boost
• Delay writing mutated assembly to after inital test is finished
• Fix NUnit and MSTest integration tests

closes #3414

[Copilot]

Pull request overview

This PR aims to improve overall runtime on large solutions by overlapping the “initial test run” phase with the project mutation phase.

Changes:

• Renamed orchestration entrypoint to MutateAndTestProjectsAsync and wired it through StrykerRunner.
• Split initialization into “create inputs” vs “run initial tests”, enabling initial tests and mutation to execute in parallel.
• Adjusted mutator behavior to enrich test-project metadata after initial tests complete, plus updated unit tests for the new flow.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/Stryker.Core/Stryker.Core/StrykerRunner.cs	Uses the new orchestrator method that performs parallel initial testing + mutation.
src/Stryker.Core/Stryker.Core/Initialisation/ProjectOrchestrator.cs	Implements the parallel execution of initial tests and mutation, and applies initial-test results after both complete.
src/Stryker.Core/Stryker.Core/Initialisation/ProjectMutator.cs	Moves initial-test enrichment out of MutateProject into a dedicated post-initial-test method.
src/Stryker.Core/Stryker.Core/Initialisation/InitialisationProcess.cs	Splits input creation from running initial tests (now returns a per-input result map).
src/Stryker.Core/Stryker.Core.UnitTest/StrykerRunnerTests.cs	Updates mocks/verifications for the renamed orchestrator API.
src/Stryker.Core/Stryker.Core.UnitTest/Initialisation/ProjectOrchestratorTests.cs	Updates tests to call the new orchestration method and stubs the enrichment call.
src/Stryker.Core/Stryker.Core.UnitTest/Initialisation/ProjectMutatorTests.cs	Ensures enrichment is invoked explicitly after mutation.
src/Stryker.Core/Stryker.Core.UnitTest/Initialisation/InitialisationProcessTests.cs	Updates tests to use the new “inputs then initial tests” API split.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.

[sonarqubecloud]

Quality Gate failed

Failed conditions
1 New Minor Issues (required ≤ 0)

See analysis details on SonarQube Cloud

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[Copilot]

Pull request overview

Copilot reviewed 15 out of 15 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 2 comments.

[Copilot]

mutationTask is created via Task.FromResult(MutateProjects(...).ToList()), which executes MutateProjects synchronously before Task.WhenAll is awaited. This means mutation exceptions will be thrown synchronously (leaving initialTestRunTask running but unobserved), and it’s also misleading because the mutation work isn’t represented as a real task. Use a real task (e.g., Task.Run(() => MutateProjects(...).ToList())) or run mutation synchronously without wrapping it and remove the WhenAll pattern.

Suggested change

	var mutationTask = Task.FromResult(MutateProjects(options, reporters, inputs).ToList());
	// Run initial test and mutation in parallel for better performance
	var mutationTask = Task.Run(() => MutateProjects(options, reporters, inputs).ToList());
	// Run initial test and mutation in parallel for better performance.

[Copilot]

executedTests.GetIdentifiers().ToHashSet() is computed even when executedTests.IsEveryTest is true, which means an unnecessary allocation on the common “every test ran” path. Consider only materializing the HashSet in the filtered branch. Also, there appears to be trailing whitespace on these lines, which can fail formatting checks depending on repo settings.

Suggested change

	var executedTestIds = executedTests.GetIdentifiers().ToHashSet();
	TestDescriptions = executedTests.IsEveryTest
	? vsTestDescriptions.ToList()
	: vsTestDescriptions.Where(p => executedTestIds.Contains(p.Id)).ToList();
	if (executedTests.IsEveryTest)
	{
	TestDescriptions = vsTestDescriptions.ToList();
	}
	else
	{
	var executedTestIds = executedTests.GetIdentifiers().ToHashSet();
	TestDescriptions = vsTestDescriptions.Where(p => executedTestIds.Contains(p.Id)).ToList();
	}