Add FailIf tests

tests/ErrorOr.ElseAsyncTests.cs

@@ -57,7 +57,7 @@ public async Task CallingElseAsyncWithValue_WhenIsSuccess_ShouldNotReturnElseVal
     }
 
     [Fact]
-    public async Task CallingElseAsyncWithValue_WhenIsError_ShouldReturnElseValue()
+    public async Task CallingElseAsyncWithValue_WhenIsError_ShouldInvokeElseFunc()
     {
         // Arrange
         ErrorOr<string> errorOrString = Error.NotFound();

tests/ErrorOr.ElseTests.cs

@@ -23,7 +23,7 @@ public void CallingElseWithValueFunc_WhenIsSuccess_ShouldNotInvokeElseFunc()
     }
 
     [Fact]
-    public void CallingElseWithValueFunc_WhenIsError_ShouldReturnElseValue()
+    public void CallingElseWithValueFunc_WhenIsError_ShouldInvokeElseFunc()
     {
         // Arrange
         ErrorOr<string> errorOrString = Error.NotFound();
@@ -57,7 +57,7 @@ public void CallingElseWithValue_WhenIsSuccess_ShouldNotReturnElseValue()
     }
 
     [Fact]
-    public void CallingElseWithValue_WhenIsError_ShouldReturnElseValue()
+    public void CallingElseWithValue_WhenIsError_ShouldInvokeElseFunc()
     {
         // Arrange
         ErrorOr<string> errorOrString = Error.NotFound();
@@ -176,7 +176,7 @@ public void CallingElseWithErrorsFunc_WhenIsSuccess_ShouldNotReturnElseErrors()
     }
 
     [Fact]
-    public async Task CallingElseWithValueAfterThenAsync_WhenIsError_ShouldReturnElseValue()
+    public async Task CallingElseWithValueAfterThenAsync_WhenIsError_ShouldInvokeElseFunc()
     {
         // Arrange
         ErrorOr<string> errorOrString = Error.NotFound();
@@ -193,7 +193,7 @@ public async Task CallingElseWithValueAfterThenAsync_WhenIsError_ShouldReturnEls
     }
 
     [Fact]
-    public async Task CallingElseWithValueFuncAfterThenAsync_WhenIsError_ShouldReturnElseValue()
+    public async Task CallingElseWithValueFuncAfterThenAsync_WhenIsError_ShouldInvokeElseFunc()
     {
         // Arrange
         ErrorOr<string> errorOrString = Error.NotFound();

tests/ErrorOr.FailIfTests.cs

@@ -0,0 +1,52 @@
+using ErrorOr;
+using FluentAssertions;
+
+namespace Tests;
+
+public class FailIfTests
+{
+    [Fact]
+    public void CallingFailIf_WhenFailsIf_ShouldReturnError()
+    {
+        // Arrange
+        ErrorOr<int> errorOrInt = 5;
+
+        // Act
+        ErrorOr<int> result = errorOrInt
+            .FailIf(num => num > 3, Error.Failure());
+
+        // Assert
+        result.IsError.Should().BeTrue();
+        result.FirstError.Type.Should().Be(ErrorType.Failure);
+    }
+
+    [Fact]
+    public void CallingFailIf_WhenDoesNotFailIf_ShouldReturnValue()
+    {
+        // Arrange
+        ErrorOr<int> errorOrInt = 5;
+
+        // Act
+        ErrorOr<int> result = errorOrInt
+            .FailIf(num => num > 10, Error.Failure());
+
+        // Assert
+        result.IsError.Should().BeFalse();
+        result.Value.Should().Be(5);
+    }
+
+    [Fact]
+    public void CallingFailIf_WhenIsError_ShouldNotInvokeFailIfFunc()
+    {
+        // Arrange
+        ErrorOr<string> errorOrString = Error.NotFound();
+
+        // Act
+        ErrorOr<string> result = errorOrString
+            .FailIf(str => str == "", Error.Failure());
+
+        // Assert
+        result.IsError.Should().BeTrue();
+        result.FirstError.Type.Should().Be(ErrorType.NotFound);
+    }
+}