Add support for single validation error with Result.Invalid

src/Ardalis.Result/Result.Void.cs

@@ -77,6 +77,16 @@ public static Result ErrorWithCorrelationId(string correlationId, params string[
             };
         }
 
+        /// <summary>
+        /// Represents the validation error that prevents the underlying service from completing.
+        /// </summary>
+        /// <param name="validationError">The validation error encountered</param>
+        /// <returns>A Result</returns>
+        public new static Result Invalid(ValidationError validationError)
+        {
+            return new Result(ResultStatus.Invalid) { ValidationErrors = { validationError } };
+        }
+
         /// <summary>
         /// Represents validation errors that prevent the underlying service from completing.
         /// </summary>

src/Ardalis.Result/Result.cs

@@ -111,6 +111,16 @@ public static Result<T> Error(params string[] errorMessages)
             return new Result<T>(ResultStatus.Error) { Errors = errorMessages };
         }
 
+        /// <summary>
+        /// Represents a validation error that prevent the underlying service from completing.
+        /// </summary>
+        /// <param name="validationError">The validation error encountered</param>
+        /// <returns>A Result<typeparamref name="T"/></returns>
+        public static Result<T> Invalid(ValidationError validationError)
+        {
+            return new Result<T>(ResultStatus.Invalid) { ValidationErrors = { validationError } };
+        }
+
         /// <summary>
         /// Represents validation errors that prevent the underlying service from completing.
         /// </summary>

tests/Ardalis.Result.UnitTests/ResultConstructor.cs

@@ -207,10 +207,18 @@ public void InitializedIsSuccessFalseForForbiddenFactoryCall()
         Assert.False(result.IsSuccess);
     }
 
+    [Fact]
+    public void InitializedIsSuccessFalseForInvalidListFactoryCall()
+    {
+        var result = Result<object>.Invalid(new List<ValidationError>());
+
+        Assert.False(result.IsSuccess);
+    }
+
     [Fact]
     public void InitializedIsSuccessFalseForInvalidFactoryCall()
     {
-        var result = Result<object>.Invalid(null);
+        var result = Result<object>.Invalid(new ValidationError());
 
         Assert.False(result.IsSuccess);
     }

tests/Ardalis.Result.UnitTests/ResultVoidConstructor.cs

@@ -1,5 +1,4 @@
 using FluentAssertions;
-using System;
 using System.Collections.Generic;
 using System.Linq;
 using Xunit;
@@ -73,7 +72,7 @@ public void InitializesErrorResultWithCorrelationIdWithFactoryMethod()
     }
 
     [Fact]
-    public void InitializesInvalidResultWithFactoryMethod()
+    public void InitializesInvalidResultWithMultipleValidationErrorsWithFactoryMethod()
     {
         var validationErrors = new List<ValidationError>
             {
@@ -98,6 +97,23 @@ public void InitializesInvalidResultWithFactoryMethod()
         result.ValidationErrors.Should().ContainEquivalentOf(new ValidationError { ErrorMessage = "PostalCode cannot exceed 10 characters", Identifier = "postalCode" });
     }
 
+    [Fact]
+    public void InitializesInvalidResultWithSingleValidationErrorWithFactoryMethod()
+    {
+        var validationError = new ValidationError
+        {
+            Identifier = "name",
+            ErrorMessage = "Name is required"
+        };
+
+        var result = Result.Invalid(validationError);
+
+        Assert.Null(result.Value);
+        Assert.Equal(ResultStatus.Invalid, result.Status);
+
+        result.ValidationErrors.Should().ContainEquivalentOf(new ValidationError { ErrorMessage = "Name is required", Identifier = "name" });
+    }
+
     [Fact]
     public void InitializesNotFoundResultWithFactoryMethod()
     {

tests/Ardalis.Result.UnitTests/ResultVoidMap.cs

@@ -1,4 +1,5 @@
 using FluentAssertions;
+using System.Collections.Generic;
 using Xunit;
 
 namespace Ardalis.Result.UnitTests
@@ -48,10 +49,21 @@ public void ShouldProduceForbidden()
             actual.Value.Should().BeNull();
         }
 
+        [Fact]
+        public void ShouldProduceInvalidWithEmptyList()
+        {
+            var result = Result.Invalid(new List<ValidationError>());
+
+            var actual = result.Map(_ => "This should be ignored");
+
+            actual.Status.Should().Be(ResultStatus.Invalid);
+            actual.Value.Should().BeNull();
+        }
+
         [Fact]
         public void ShouldProduceInvalid()
         {
-            var result = Result.Invalid(new());
+            var result = Result.Invalid(new ValidationError());
 
             var actual = result.Map(_ => "This should be ignored");
 

tests/Ardalis.Result.UnitTests/ResultVoidToResultOfT.cs

@@ -23,7 +23,7 @@ public void ConvertFromErrorResultOfUnit(params string[] errors)
     }
 
     [Fact]
-    public void ConvertFromInvalidResultOfUnit()
+    public void ConvertFromInvalidResultOfUnitWithValidationErrorList()
     {
         var validationErrors = new List<ValidationError>
             {
@@ -49,6 +49,24 @@ public void ConvertFromInvalidResultOfUnit()
         result.ValidationErrors.Should().ContainEquivalentOf(new ValidationError { ErrorMessage = "PostalCode cannot exceed 10 characters", Identifier = "postalCode" });
     }
 
+    [Fact]
+    public void ConvertFromInvalidResultOfUnitWithValidationError()
+    {
+        var validationError = new ValidationError
+        {
+            Identifier = "name",
+            ErrorMessage = "Name is required"
+        };
+
+        var result = DoBusinessOperationExample<object>(Result.Invalid(validationError));
+
+        Assert.Null(result.Value);
+        Assert.Equal(ResultStatus.Invalid, result.Status);
+
+        result.Status.Should().Be(ResultStatus.Invalid);
+        result.ValidationErrors.Should().ContainEquivalentOf(new ValidationError { ErrorMessage = "Name is required", Identifier = "name" });
+    }
+
     [Fact]
     public void ConvertFromNotFoundResultOfUnit()
     {