perf: use shared Task.FromResult(Passed)

[TimothyMakkison]

Use return a shared static Task.FromResult(Passed) for successful assertions. This should be safe because AssertionResult is a readonly struct

Before

After

[thomhurst]

Summary

This PR introduces a shared static cached Task<AssertionResult> for successful assertions to reduce allocations in the hot path.

Critical Issues

CRITICAL: Static field initialization bug ⚠️

The new field in AssertionResult.cs:8:

internal static Task<AssertionResult> _passedTask = Task.FromResult(Passed);

This creates a static initialization order issue. The _passedTask field references the Passed property, but C# doesn't guarantee the order of static field initializers. Since Passed is a property (not a field), this should work, but it's fragile.

More importantly: The Passed property creates a new instance on every access:

public static AssertionResult Passed => new(true, string.Empty);

This means _passedTask is initialized with a Task<AssertionResult> containing one instance, but later direct uses of AssertionResult.Passed create different instances. While this works because AssertionResult is a readonly struct with value semantics, it's confusing.

Recommendation: Make the initialization explicit and safe:

internal static readonly Task<AssertionResult> _passedTask = Task.FromResult(new AssertionResult(true, string.Empty));

And add readonly modifier for thread safety (static fields should be readonly when immutable).

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Minor: Field naming convention

The field _passedTask uses underscore prefix which typically indicates instance fields in C#. For static fields, consider s_passedTask or PassedTask (if keeping it internal).

Suggestions

1. Consider readonly modifier: Since this is a shared static field accessed from multiple threads (assertions run concurrently), marking it readonly makes the immutability contract explicit and prevents accidental reassignment.

2. Performance validation: The PR shows impressive allocation improvements in the screenshots. Consider adding a comment in the code explaining this optimization for future maintainers.

Verdict

⚠️ REQUEST CHANGES - Fix static initialization to avoid fragile dependency on property access order

[TimothyMakkison]

CRITICAL: Static field initialization bug ⚠️

Since Passed is a property (not a field), this should work, but it's fragile.

Minor: Field naming convention

Name 'PassedTask' does not match rule 'camel_case_for_private_internal_fields'. Suggested name is '_passedTask'.