MSTEST0062: Avoid out and ref parameters in test methods

Cause

A test method has parameters marked with out or ref modifiers.

Rule description

Test methods should not have out or ref parameters. MSTest is responsible for calling test methods, and it never reads the values that are passed by reference after the test method finishes. These modifiers are misleading because they suggest the test method returns values that will be used, but MSTest never uses them after the test completes.

[TestClass]
public class TestClass
{
    [TestMethod]
    public void TestMethod(out string s, ref string s2) // Violation
    {
        s = "test";
    }
}

How to fix violations

Remove the out and ref modifiers from test method parameters.

[TestClass]
public class TestClass
{
    [TestMethod]
    public void TestMethod()
    {
        // Test code
    }
}

If you need to test methods with out or ref parameters, call them from within your test method:

[TestClass]
public class TestClass
{
    [TestMethod]
    public void TestMethodWithOutParameter()
    {
        // Arrange
        string result;
        string passedByRef = "some value";
        var instance = new MyClass();
        
        // Act
        bool success = instance.TryGetValue(out result, ref passedByRef);
        
        // Assert
        Assert.IsTrue(success);
        Assert.AreEqual("expected", result);
    }
}

For data-driven tests:

[TestClass]
public class TestClass
{
    [TestMethod]
    [DataRow("input1", "expected1")]
    [DataRow("input2", "expected2")]
    public void TestMethod(string input, string expected)
    {
        // Arrange
        string result;
        var instance = new MyClass();
        
        // Act
        bool success = instance.TryParse(input, out result);
        
        // Assert
        Assert.IsTrue(success);
        Assert.AreEqual(expected, result);
    }
}

When to suppress warnings

Do not suppress warnings from this rule. There is no valid scenario where test methods should use out or ref parameters.

Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable MSTEST0062
// The code that's violating the rule is on this line.
#pragma warning restore MSTEST0062

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.MSTEST0062.severity = none

For more information, see How to suppress code analysis warnings.