Remove async-without-await warnings in CoreAssertionFixture

Author: yevhen

CLAUDE.md

@@ -418,3 +418,4 @@ async\method: Suffix with `Async` =\> `GetDataAsync()`
 
 - Expression compilation can emit invalid IL on some runtimes; fall back to `Compile(preferInterpretation: true)` when evaluating expressions to avoid CI-only `InvalidProgramException`.
 - Byref-like expression trees (e.g., `Span<T>`, `ReadOnlySpan<T>`) cannot be boxed; convert them to arrays before evaluation to avoid interpreter type load errors.
+- `NUnit.Assert.ThrowsAsync<T>()` returns the exception instance (not a `Task`), so async tests should await a real async assertion (e.g., `action.Should().ThrowAsync<T>()`) to avoid CS1998 warnings.

learnings.md

@@ -129,6 +129,7 @@ This document is organized by topic to consolidate key learnings about the proje
 - **DynamicInvoke Cross-Platform Issues:** Using `Expression.Lambda(expression).Compile().DynamicInvoke()` can fail on CI/certain runtimes with `NotSupportedException: Specified method is not supported` - use strongly-typed `Expression.Lambda<Func<object>>(Expression.Convert(expression, typeof(object))).Compile()()` for direct invocation without reflection
 - **Expression.Compile InvalidProgramException:** Expression compilation can emit invalid IL on some runtimes; prefer `Compile(preferInterpretation: true)` or catch `InvalidProgramException` and recompile in interpreted mode to ensure value extraction works on CI
 - **ByRef-like expression evaluation:** Ref structs (e.g., `Span<T>`, `ReadOnlySpan<T>`) cannot be boxed to `object`; convert them to arrays (e.g., `MemoryExtensions.ToArray`) before value extraction to avoid interpreter `TypeLoadException`/`ArgumentException`.
+- **NUnit Assert.ThrowsAsync return type:** `Assert.ThrowsAsync<T>()` returns the exception instance, not a `Task`, so async test methods need an explicit awaitable (e.g., `action.Should().ThrowAsync<T>()`) to avoid CS1998 warnings.
 
 ## String Diffing Implementation (Increment 5)
 

src/SharpAssert.Tests/CoreAssertionFixture.cs

@@ -101,19 +101,20 @@ public async Task ThrowsAsync_should_pass_when_expected_exception()
                 throw new InvalidOperationException();
             });
 
-            var action = async () => Assert(result);
-            await action.Should().NotThrowAsync();
+            Action action = () => Assert(result);
+            action.Should().NotThrow();
         }
 
         [Test]
         public async Task ThrowsAsync_should_fail_wrong_type()
         {
-            NUnit.Framework.Assert.ThrowsAsync<SharpAssertionException>(async () => 
-                await ThrowsAsync<NullReferenceException>(async () => 
-                {
-                    await Task.Yield();
-                    throw new ArgumentException();
-                }));
+            var action = async () => await ThrowsAsync<NullReferenceException>(async () => 
+            {
+                await Task.Yield();
+                throw new ArgumentException();
+            });
+
+            await action.Should().ThrowAsync<SharpAssertionException>();
         }
     }
 }