#16 - Preserve PreconditionFailed message when mapping to other type (#17)

- Fixes issue where mapping a PreconditionFailedResult<T> to another
type loses the message.
- Adds unit test to ensure reason and message are preserved when mapping
to other failure type.

Fixes #16

Co-authored-by: Mitch Lienau <mitch@feature23.com>

Author: mlienau

src/F23.Kernel.Tests/Results/PreconditionFailedResultTests.cs

@@ -15,5 +15,28 @@ public void PreconditionFailedResult_SuccessIsFalse(PreconditionFailedReason rea
 
         // Assert
         Assert.False(result.IsSuccess);
+    }
+
+    [Theory]
+    [InlineData(PreconditionFailedReason.NotFound)]
+    [InlineData(PreconditionFailedReason.ConcurrencyMismatch)]
+    [InlineData(PreconditionFailedReason.Conflict)]
+    public void MappingPreconditionFailedResultToOther_PreservesTheReasonAndMessage(PreconditionFailedReason reason)
+    {
+        // Arrange
+        var originalMessage = "Original failure message";
+        var originalResult = new PreconditionFailedResult<Original>(reason, originalMessage);
+
+        // Act
+        var mappedResult = originalResult.MapFailure<Other>();
+
+        // Assert
+        var preconditionFailedResult = Assert.IsType<PreconditionFailedResult<Other>>(mappedResult);
+        Assert.Equal(reason, preconditionFailedResult.Reason);
+        Assert.Equal(originalMessage, preconditionFailedResult.Message);
     }
+
+    private class Original { }
+
+    private class Other { }
 }

src/F23.Kernel/Result.cs

@@ -151,7 +151,7 @@ public Result<TOther> MapFailure<TOther>() =>
             SuccessResult<T> => throw new InvalidOperationException("Cannot map failure on success result"),
             ValidationFailedResult<T> validationFailed => Result<TOther>.ValidationFailed(validationFailed.Errors),
             UnauthorizedResult<T> unauthorized => Result<TOther>.Unauthorized(unauthorized.Message),
-            PreconditionFailedResult<T> preconditionFailed => Result<TOther>.PreconditionFailed(preconditionFailed.Reason),
+            PreconditionFailedResult<T> preconditionFailed => Result<TOther>.PreconditionFailed(preconditionFailed.Reason, preconditionFailed.Message),
             _ => throw new InvalidOperationException("Unknown result type")
         };