Add Extension Methods to Assert in MSTest

An extendible implementation of the Assert class in MSTest. Allows for extending the Assert methods whilst retaining the default Assert methods. Also includes a Throws() method for asserting exceptions.

What Problem Does it Solve?

I wanted to be able to add my own extension methods to Assert e.g. Assert.Throws() but keeping the existing default MSTest methods.

e.g.

[TestMethod]
public void AddWithNegativeNumberThrowsExceptionExpectedMessage()
{
    // Arrange
    StringCalculator sc = new StringCalculator();

    // Act => Assert
    Assert.Throws(() => sc.Add("-1"), "you cannot supply negative numbers.");
}

To accommodate such syntax I had to write this wrapper.

Get Started

1. Add the MsTestExtensions.dll lib to your project. (I'm assuming you may have downloaded the package from Nuget to do this: package name = MsTestExtensions.)

2. Add a using/import MsTestExtensions entry within your class.

3. Inherit from BaseTest with the Test Class you are using and you should see Assert.Throws(...) in intellisense.

   • If you would rather not inherit from BaseTest you can use the syntax:
     • ThrowsAssert.Throws(...)
     • ThrowsAsyncAssert.Throws(...)
   • Lastly if the above options do not suite, you can add the following within your test class: public static readonly IAssertion Assert = new Assertion();

NB: IAssertion is the interface to use for adding your own custom extensions.

For more details see the accompanying blog post.

Features

Assert Exceptions are thrown

• Assert.Throws()
• Assert.ThrowsAsync()

Example:

Assert.Throws(() => { throw new Exception(); });

Assert an Exception Type

Assert.Throws<T>()
Assert.ThrowsAsync<T>()

Where the type T must be the exception type. Example:

Assert.Throws<ArgumentNullException>(() => { throw ArgumentNullException(); });

There are options to assert the exception type:

• Inherits (the default case - a type will pass the assertion if it is a subtype)
• Exact (subclasses are not considered - See example)

Assert an Exception Message

It is possible to assert the message of the exception. Example:

Assert.Throws(() => { throw new ArgumentNullException("username"); }, "Value cannot be null." + Environment.NewLine + "Parameter name: username";);

There are options to assert the exception message:

• Exact (the default case)
• Contains (for partial matching - See example)
• IgnoreCase (case of string is ignored - See example)

For more examples, see the unit tests: https://github.com/bbraithwaite/MSTestExtensions/blob/master/src/MSTestExtensions.Tests/ThrowsTests.cs

Versioning

Latest version is 4.0.0.

Available via Nuget: https://www.nuget.org/packages/MSTestExtensions/4.0.0

License

MIT license - http://www.opensource.org/licenses/mit-license.php

Related

In the mean time ThrowsException and ThrowsExceptionAsync are included in Micorosft MSTest V2.