feat: enhance assertion exception messages to include inline 'because' reasons

TUnit.Assertions.Tests/AssertConditions/BecauseTests.cs

@@ -144,4 +144,26 @@ await Assert.That(variable).IsFalse().Because(because1)
         var exception = await Assert.ThrowsAsync<AssertionException>(action);
         await Assert.That(exception.Message).Contains(because1).And.Contains(because2);
     }
+
+    [Test]
+    public async Task Because_Message_Appears_Inline_With_Expectation()
+    {
+        var expectedMessage = """
+                              Expected to be false, because this is the reason
+                              but found True
+
+                              at Assert.That(variable).IsFalse().Because("this is the reason")
+                              """;
+
+        var variable = true;
+
+        var action = async () =>
+        {
+            await Assert.That(variable).IsFalse().Because("this is the reason");
+        };
+
+        var exception = await Assert.ThrowsAsync<AssertionException>(action);
+        await Assert.That(exception.Message.NormalizeLineEndings())
+            .IsEqualTo(expectedMessage.NormalizeLineEndings());
+    }
 }

TUnit.Assertions/Core/Assertion.cs

@@ -212,22 +212,24 @@ public OrContinuation<TValue> Or
     /// </summary>
     protected Exception CreateException(AssertionResult result)
     {
-        var message = $"""
-            Expected {GetExpectation()}
-            but {result.Message}
-
-            at {Context.ExpressionBuilder}
-            """;
+        var expectation = GetExpectation();
 
         if (_becauseMessage != null)
         {
-            // Check if message already starts with "because" to avoid duplication
+            // Append because message inline with the expectation
             var becausePrefix = _becauseMessage.StartsWith("because ", StringComparison.OrdinalIgnoreCase)
                 ? _becauseMessage
                 : $"because {_becauseMessage}";
-            message += $"\n\n{becausePrefix}";
+            expectation = $"{expectation}, {becausePrefix}";
         }
 
+        var message = $"""
+            Expected {expectation}
+            but {result.Message}
+
+            at {Context.ExpressionBuilder}
+            """;
+
         return new AssertionException(message);
     }