Add unittests

src/backend/tests/unit/Common/ResultTests.cs

@@ -0,0 +1,53 @@
+using Randall.Domain.Common;
+
+namespace Randall.Domain.UnitTests.Common;
+
+public class ResultTests
+{
+    [Fact]
+    public void Success_IsSuccessIsTrue()
+    {
+        var result = Result.Success();
+
+        Assert.True(result.IsSuccess);
+        Assert.Null(result.Error);
+    }
+
+    [Fact]
+    public void Failure_IsSuccessIsFalse()
+    {
+        var result = Result.Failure("Something went wrong");
+
+        Assert.False(result.IsSuccess);
+        Assert.Equal("Something went wrong", result.Error);
+    }
+
+    [Fact]
+    public void SuccessOfT_ContainsValue()
+    {
+        var result = Result.Success(42);
+
+        Assert.True(result.IsSuccess);
+        Assert.Equal(42, result.Value);
+        Assert.Null(result.Error);
+    }
+
+    [Fact]
+    public void FailureOfT_ValueIsDefault()
+    {
+        var result = Result.Failure<int>("error");
+
+        Assert.False(result.IsSuccess);
+        Assert.Equal(default, result.Value);
+        Assert.Equal("error", result.Error);
+    }
+
+    [Fact]
+    public void FailureOfT_ReferenceType_ValueIsNull()
+    {
+        var result = Result.Failure<string>("error");
+
+        Assert.False(result.IsSuccess);
+        Assert.Null(result.Value);
+    }
+}