Add AppendErrors method to OperationResult<TResult> and related tests

Author: Svetlozar Stoykov

src/OneBitSoftware.Utilities.OperationResult/OperationResult.cs

@@ -295,6 +295,17 @@ public OperationResult(TResult resultObject) : base()
         /// </summary>
         public TResult? ResultObject { get; set; }
 
+        /// <summary>
+        /// Appends error from <paramref name="otherOperationResult"/> to the current instance.
+        /// </summary>
+        /// <param name="otherOperationResult">The <see cref="OperationResult"/> to append from.</param>
+        /// <returns>The original <see cref="OperationResult"/> with the appended messages from <paramref name="otherOperationResult"/>.</returns>
+        public new OperationResult<TResult> AppendErrors(OperationResult? otherOperationResult)
+        {
+            base.AppendErrors(otherOperationResult);
+            return this;
+        }
+
         /// <summary>
         /// This method will append an error with a specific `user-friendly` message to this operation result instance.
         /// </summary>

tests/OneBitSoftware.Utilities.OperationResultTests/OperationResultAppendErrorsTests.cs

@@ -177,4 +177,78 @@ public void AppendErrors_ShouldLogWhenCreatedWithNoLogger()
         // Assert
         Assert.Equal(1, testLogger.LogMessages.Count);
     }
+
+    [Fact]
+    public void AppendErrors_NonGenericSource_To_GenericTarget_Retains_Generic_Type_And_MergesErrors()
+    {
+        // Arrange
+        var source = new OperationResult();
+        source.AppendError("E1", 101, LogLevel.Warning, "D1");
+
+        var target = new OperationResult<string>();
+        target.AppendError("E0", 100, LogLevel.Information, "D0");
+
+        // Act
+        var returned = target.AppendErrors(source);
+
+        // Assert
+        Assert.Same(target, returned);
+        Assert.True(target.Fail);
+        Assert.Equal(2, target.Errors.Count);
+        Assert.NotNull(target.Errors.Single(e => e is { Code: 100, Message: "E0" }));
+        Assert.NotNull(target.Errors.Single(e => e is { Code: 101, Message: "E1" }));
+    }
+
+    [Fact]
+    public void AppendErrors_GenericSource_To_GenericTarget_Retains_Generic_Type_And_MergesErrors()
+    {
+        // Arrange
+        var source = new OperationResult<double>();
+        source.AppendError("E1", 101, LogLevel.Warning, "D1");
+
+        var target = new OperationResult<string>();
+        target.AppendError("E0", 100, LogLevel.Information, "D0");
+
+        // Act
+        var returned = target.AppendErrors(source);
+
+        // Assert
+        Assert.Same(target, returned);
+        Assert.True(target.Fail);
+        Assert.Equal(2, target.Errors.Count);
+        Assert.NotNull(target.Errors.Single(e => e is { Code: 100, Message: "E0" }));
+        Assert.NotNull(target.Errors.Single(e => e is { Code: 101, Message: "E1" }));
+    }
+
+    [Fact]
+    public void AppendErrors_WithNullSource_On_NonGenericTarget_Returns_Same_Instance_And_NoChange()
+    {
+        // Arrange
+        var target = new OperationResult();
+        target.AppendError("E0", 100, LogLevel.Information, "D0");
+        var beforeCount = target.Errors.Count;
+
+        // Act
+        var returned = target.AppendErrors(null);
+
+        // Assert
+        Assert.Same(target, returned);
+        Assert.Equal(beforeCount, target.Errors.Count);
+    }
+
+    [Fact]
+    public void AppendErrors_WithNullSource_On_GenericTarget_Returns_Same_Instance_And_NoChange()
+    {
+        // Arrange
+        var target = new OperationResult<object>();
+        target.AppendError("E0", 100, LogLevel.Information, "D0");
+        var beforeCount = target.Errors.Count;
+
+        // Act
+        var returned = target.AppendErrors((OperationResult)null);
+
+        // Assert
+        Assert.Same(target, returned);
+        Assert.Equal(beforeCount, target.Errors.Count);
+    }
 }