perf(assertions): avoid eager interpolated-string alloc in assertion source ctors

TUnit.Assertions/Sources/ArrayAssertion.cs

@@ -30,8 +30,6 @@ internal ArrayAssertion(AssertionContext<TItem[]> context)
 
     private static StringBuilder CreateExpressionBuilder(string? expression)
     {
-        var builder = new StringBuilder();
-        builder.Append($"Assert.That({expression ?? "?"})");
-        return builder;
+        return new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
     }
 }

TUnit.Assertions/Sources/AsyncDelegateAssertion.cs

@@ -25,8 +25,7 @@ public class AsyncDelegateAssertion : IAssertionSource<object?>, IDelegateAssert
     public AsyncDelegateAssertion(Func<Task> action, string? expression)
     {
         AsyncAction = action ?? throw new ArgumentNullException(nameof(action));
-        var expressionBuilder = new StringBuilder();
-        expressionBuilder.Append($"Assert.That({expression ?? "?"})");
+        var expressionBuilder = new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
         var evaluationContext = new EvaluationContext<object?>(async () =>
         {
             try
@@ -42,8 +41,7 @@ public AsyncDelegateAssertion(Func<Task> action, string? expression)
         Context = new AssertionContext<object?>(evaluationContext, expressionBuilder);
 
         // DO NOT await the task here - we want to check its state synchronously
-        var taskExpressionBuilder = new StringBuilder();
-        taskExpressionBuilder.Append(expressionBuilder.ToString());
+        var taskExpressionBuilder = new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
         var taskEvaluationContext = new EvaluationContext<Task>(() =>
         {
             // This allows IsCompleted, IsCanceled, IsFaulted, etc. to check task properties synchronously

TUnit.Assertions/Sources/AsyncEnumerableAssertion.cs

@@ -24,8 +24,7 @@ private static AssertionContext<IAsyncEnumerable<TItem>> CreateContext(
         IAsyncEnumerable<TItem> value,
         string? expression)
     {
-        var expressionBuilder = new StringBuilder();
-        expressionBuilder.Append($"Assert.That({expression ?? "?"})");
+        var expressionBuilder = new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
         return new AssertionContext<IAsyncEnumerable<TItem>>(value, expressionBuilder);
     }
 }

TUnit.Assertions/Sources/AsyncFuncAssertion.cs

@@ -16,8 +16,7 @@ public class AsyncFuncAssertion<TValue> : IAssertionSource<TValue>, IDelegateAss
 
     public AsyncFuncAssertion(Func<Task<TValue?>> func, string? expression)
     {
-        var expressionBuilder = new StringBuilder();
-        expressionBuilder.Append($"Assert.That({expression ?? "?"})");
+        var expressionBuilder = new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
         var evaluationContext = new EvaluationContext<TValue>(async () =>
         {
             try

TUnit.Assertions/Sources/AsyncFuncCollectionAssertion.cs

@@ -19,8 +19,7 @@ public AsyncFuncCollectionAssertion(Func<Task<IEnumerable<TItem>?>> func, string
 
     private static AssertionContext<IEnumerable<TItem>> CreateContext(Func<Task<IEnumerable<TItem>?>> func, string? expression)
     {
-        var expressionBuilder = new StringBuilder();
-        expressionBuilder.Append($"Assert.That({expression ?? "?"})");
+        var expressionBuilder = new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
         var evaluationContext = new EvaluationContext<IEnumerable<TItem>>(async () =>
         {
             try

TUnit.Assertions/Sources/CollectionAssertion.cs

@@ -31,8 +31,6 @@ internal CollectionAssertion(AssertionContext<IEnumerable<TItem>> context)
 
     private static StringBuilder CreateExpressionBuilder(string? expression)
     {
-        var builder = new StringBuilder();
-        builder.Append($"Assert.That({expression ?? "?"})");
-        return builder;
+        return new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
     }
 }

TUnit.Assertions/Sources/DelegateAssertion.cs

@@ -19,8 +19,7 @@ public class DelegateAssertion : IAssertionSource<object?>, IDelegateAssertionSo
     public DelegateAssertion(Action action, string? expression)
     {
         Action = action ?? throw new ArgumentNullException(nameof(action));
-        var expressionBuilder = new StringBuilder();
-        expressionBuilder.Append($"Assert.That({expression ?? "?"})");
+        var expressionBuilder = new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
         var evaluationContext = new EvaluationContext<object?>(() =>
         {
             try

TUnit.Assertions/Sources/DictionaryAssertion.cs

@@ -29,8 +29,7 @@ private static AssertionContext<IReadOnlyDictionary<TKey, TValue>> CreateContext
         IReadOnlyDictionary<TKey, TValue>? value,
         string? expression)
     {
-        var expressionBuilder = new StringBuilder();
-        expressionBuilder.Append($"Assert.That({expression ?? "?"})");
+        var expressionBuilder = new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
         return new AssertionContext<IReadOnlyDictionary<TKey, TValue>>(value!, expressionBuilder);
     }
 }

TUnit.Assertions/Sources/FuncAssertion.cs

@@ -16,8 +16,7 @@ public class FuncAssertion<TValue> : IAssertionSource<TValue>, IDelegateAssertio
 
     public FuncAssertion(Func<TValue?> func, string? expression)
     {
-        var expressionBuilder = new StringBuilder();
-        expressionBuilder.Append($"Assert.That({expression ?? "?"})");
+        var expressionBuilder = new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
         var evaluationContext = new EvaluationContext<TValue>(() =>
         {
             try

TUnit.Assertions/Sources/FuncCollectionAssertion.cs

@@ -19,8 +19,7 @@ public FuncCollectionAssertion(Func<IEnumerable<TItem>?> func, string? expressio
 
     private static AssertionContext<IEnumerable<TItem>> CreateContext(Func<IEnumerable<TItem>?> func, string? expression)
     {
-        var expressionBuilder = new StringBuilder();
-        expressionBuilder.Append($"Assert.That({expression ?? "?"})");
+        var expressionBuilder = new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
         var evaluationContext = new EvaluationContext<IEnumerable<TItem>>(() =>
         {
             try

TUnit.Assertions/Sources/ListAssertion.cs

@@ -34,8 +34,7 @@ private static AssertionContext<IList<TItem>> CreateContext(
         IList<TItem>? value,
         string? expression)
     {
-        var expressionBuilder = new StringBuilder();
-        expressionBuilder.Append($"Assert.That({expression ?? "?"})");
+        var expressionBuilder = new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
         return new AssertionContext<IList<TItem>>(value!, expressionBuilder);
     }
 }

TUnit.Assertions/Sources/MemoryAssertion.cs

@@ -37,9 +37,7 @@ private protected MemoryAssertion(AssertionContext<Memory<TItem>> context)
 
     private static StringBuilder CreateExpressionBuilder(string? expression)
     {
-        var builder = new StringBuilder();
-        builder.Append($"Assert.That({expression ?? "?"})");
-        return builder;
+        return new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
     }
 }
 
@@ -74,9 +72,7 @@ private protected ReadOnlyMemoryAssertion(AssertionContext<ReadOnlyMemory<TItem>
 
     private static StringBuilder CreateExpressionBuilder(string? expression)
     {
-        var builder = new StringBuilder();
-        builder.Append($"Assert.That({expression ?? "?"})");
-        return builder;
+        return new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
     }
 }
 #endif

TUnit.Assertions/Sources/MutableDictionaryAssertion.cs

@@ -31,8 +31,7 @@ private static AssertionContext<IDictionary<TKey, TValue>> CreateContext(
         IDictionary<TKey, TValue>? value,
         string? expression)
     {
-        var expressionBuilder = new StringBuilder();
-        expressionBuilder.Append($"Assert.That({expression ?? "?"})");
+        var expressionBuilder = new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
         return new AssertionContext<IDictionary<TKey, TValue>>(value!, expressionBuilder);
     }
 }

TUnit.Assertions/Sources/ReadOnlyListAssertion.cs

@@ -30,8 +30,7 @@ private static AssertionContext<IReadOnlyList<TItem>> CreateContext(
         IReadOnlyList<TItem>? value,
         string? expression)
     {
-        var expressionBuilder = new StringBuilder();
-        expressionBuilder.Append($"Assert.That({expression ?? "?"})");
+        var expressionBuilder = new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
         return new AssertionContext<IReadOnlyList<TItem>>(value!, expressionBuilder);
     }
 }

TUnit.Assertions/Sources/SetAssertion.cs

@@ -43,9 +43,7 @@ private protected SetAssertion(AssertionContext<ISet<TItem>> context)
 
     private static StringBuilder CreateExpressionBuilder(string? expression)
     {
-        var builder = new StringBuilder();
-        builder.Append($"Assert.That({expression ?? "?"})");
-        return builder;
+        return new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
     }
 }
 
@@ -88,9 +86,7 @@ private protected ReadOnlySetAssertion(AssertionContext<IReadOnlySet<TItem>> con
 
     private static StringBuilder CreateExpressionBuilder(string? expression)
     {
-        var builder = new StringBuilder();
-        builder.Append($"Assert.That({expression ?? "?"})");
-        return builder;
+        return new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
     }
 }
 #endif
@@ -133,8 +129,6 @@ private protected HashSetAssertion(AssertionContext<HashSet<TItem>> context)
 
     private static StringBuilder CreateExpressionBuilder(string? expression)
     {
-        var builder = new StringBuilder();
-        builder.Append($"Assert.That({expression ?? "?"})");
-        return builder;
+        return new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
     }
 }

TUnit.Assertions/Sources/TaskAssertion.cs

@@ -21,8 +21,7 @@ public class TaskAssertion<TValue> : IAssertionSource<TValue>, IDelegateAssertio
 
     public TaskAssertion(Task<TValue?> task, string? expression)
     {
-        var expressionBuilder = new StringBuilder();
-        expressionBuilder.Append($"Assert.That({expression ?? "?"})");
+        var expressionBuilder = new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
 
         // Context for result assertions (e.g., IsEqualTo on the TValue result)
         var evaluationContext = new EvaluationContext<TValue>(async () =>
@@ -41,8 +40,7 @@ public TaskAssertion(Task<TValue?> task, string? expression)
 
         // Context for task state assertions (e.g., IsCompleted on the Task<TValue>)
         // DO NOT await the task here - we want to check its state synchronously
-        var taskExpressionBuilder = new StringBuilder();
-        taskExpressionBuilder.Append(expressionBuilder.ToString());
+        var taskExpressionBuilder = new StringBuilder("Assert.That(").Append(expression ?? "?").Append(')');
         var taskEvaluationContext = new EvaluationContext<Task<TValue?>>(() =>
         {
             // Return the task object itself without awaiting it