MSTEST0063: Test classes should have valid constructors

Property	Value
Rule ID	MSTEST0063
Title	Test classes should have valid constructors
Category	Usage
Fix is breaking or non-breaking	Non-breaking
Enabled by default	Yes
Default severity	Warning
Introduced in version	4.1.0
Is there a code fix	No

Cause

A test class doesn't have a valid constructor. Valid constructors are public and either parameterless or have a single parameter of type TestContext.

Rule description

Test classes must have a public constructor that is either parameterless or accepts a single TestContext parameter. This allows the test framework to instantiate the test class properly.

Constructors that are non-public, have parameters of unsupported types, or have multiple parameters aren't valid and prevent the test framework from creating instances of the test class.

[TestClass]
public class MyTestClass
{
    private MyTestClass() // Violation - constructor is not public
    {
    }
}

[TestClass]
public class MyTestClass
{
    public MyTestClass(string value) // Violation - parameter type is not supported
    {
    }
}

[TestClass]
public class MyTestClass
{
    public MyTestClass(TestContext testContext, int value) // Violation - multiple parameters
    {
    }
}

How to fix violations

Ensure your test class has a valid constructor. A valid constructor must be:

1. Declared as public.
2. Either parameterless or accepts a single TestContext parameter.

Parameterless constructor

[TestClass]
public class MyTestClass
{
    public MyTestClass()
    {
    }

    [TestMethod]
    public void TestMethod()
    {
    }
}

Constructor with TestContext

[TestClass]
public class MyTestClass
{
    private readonly TestContext _testContext;

    public MyTestClass(TestContext testContext)
    {
        _testContext = testContext;
    }

    [TestMethod]
    public void TestMethod()
    {
        _testContext.WriteLine("Test is running...");
    }
}

Implicit parameterless constructor

If you don't define any constructor, the compiler generates a public parameterless constructor automatically:

[TestClass]
public class MyTestClass
{
    [TestMethod]
    public void TestMethod()
    {
    }
}

Valid and invalid constructors together

If your test class has multiple constructors, at least one must be valid:

[TestClass]
public class MyTestClass
{
    public MyTestClass() // Valid - this makes the class valid
    {
    }

    private MyTestClass(int x) // Invalid, but ignored because a valid constructor exists
    {
    }

    [TestMethod]
    public void TestMethod()
    {
    }
}

When to suppress warnings

Don't suppress warnings from this rule. Test classes without valid constructors can't be instantiated by the test framework, and the tests won't run.

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 MSTEST0063
// The code that's violating the rule is on this line.
#pragma warning restore MSTEST0063

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

[*.{cs,vb}]
dotnet_diagnostic.MSTEST0063.severity = none

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