Ockham.Test

A small set of framework-agnostic unit testing utilities. Part of the Ockham.Net project.

The Problem

Every Ockham component should solve a clear problem that is not solved in the .Net BCL, or in the particular libraries it is meant to augment.

The utilities in this library address two simple problems encountered when unit testing:

• Testing exception properties
• Testing non-public methods

1. Assert.Throws: Testing exception messages against patterns, arbitrary exception properties

All major .Net unit testing frameworks provide simple, semantic mechanisms for testing for expected exceptions of a particular type. They do not provide means of testing the contents of the exception message, or other properties on the exception. The overloads of Ockham.Test.Assert.Throws provide mechanisms for doing one or both of these things.

The point here is that the content of error messages and / or additional information attached to an exception represent testable requirements in and of themselves. Such requirements can be tested by hand:

[Test/Fact/TestMethod/etc.]
public void ExceptionTest() 
{
    bool exceptionWasThrown = false;
    try 
    {
        /* do stuff */
    } 
    catch (ExpectedExceptionType ex) 
    {
        exceptionWasThrown = true;

        // TEST: Was the correct helpful exception message produced?
        Assert.True(Regex.IsMatch(ex.Message, @"some pattern"));

        // TEST: Was the HelpfulProperty correctly set?
        Assert.Equal("expected value", ex.HelpfulProperty)
    }

    Assert.True(exceptionWasThrown); 
}

Writing this more succinctly and semantically is helpful for the same reason that all the frameworks provide a succinct way of testing for an expected exception by type

[Test/Fact/TestMethod/etc.]
public void ExceptionTest() 
{
    // Simple test for message pattern is still just one line
    Ockham.Test.Assert.Throws(() => /* do stuff */, @"some pattern");

    // So is a test for a single arbitrary assertion about the exception itself
    Ockham.Test.Assert.Throws(() => /* do stuff */, ex => Assert.Equal("expected value", ex.HelpfulProperty));

    // It may be a matter of taste whether the following is more or less "readable" than the long form:
    Ockham.Test.Assert.Throws(() => /* do stuff */, @"some pattern", ex => {
        Assert.Equal("expected value", ex.HelpfulProperty);
        Assert.NotNull(ex.ImportantData);
    });
}

2. MethodReflection: Testing private and protected methods

Yes, yes, in general you should not need to test private and protected methods. They are implementation details irrelevant to the testable public surface area of your code.

Except when they are not. Like when you want to compose the public surface area from several important but private / protected / internal components. A good example is the private static _To method in the Ockham.Data.Convert class, defined in the Ockham.Data module. It provides a single, consolidated logic for fast but flexible basic data type conversions, but its full signature is not meant to be public. Instead, a wide range of public methods expose different variations of the underlying conversion logic. That project includes a wide array of tests on those public conversion APIs, but it ALSO include lots of tests to ensure that this single crucial method works exactly as intended.

The static Ockham.Test.MethodReflection class provides simple ways of generating callable delegates for non-public methods by matching the signature against a strongly typed delegate. The idea here is you wrote the code, so you know the details of the method you want to test. In fact, you can mostly copy and paste the signature of the actual method into your test class, replace the access keyword with 'delegate', and you are good to go:

// In some useful class
public static class VeryUseful {
    private static bool _Implementation(int someArg, string anotherArg, Dictionary<long, Thing> thingMap, out failureMessage) {
        /* code ... */
    }

    protected string DoStuff(int someArg, string anotherArg, params Thing[] things) {
        /* code ... */
    }
}

// In your test class
public class VeryUsefulTests {
    
    // Copied and pasted from VeryUseful.cs:
    delegate bool _Implementation(int someArg, string anotherArg, Dictionary<long, Thing> thingMap, out failureMessage);
    delegate bool ImplementationDelegate(int someArg, string anotherArg, Dictionary<long, Thing> thingMap, out failureMessage);
    delegate string DoStuff(int someArg, string anotherArg, params Thing[] things);

    [Test/Fact/TestMethod/etc.]
    public void Implementation_Case1() 
    {
        // If the name of the delegate type matches the target method, you don't need to provide the name
        var _impl = Ockham.Test.MethodReflection.GetMethodCaller<_Implementation, VeryUseful>();

        // But you can always specify the name explicitly
        var impl2 = Ockham.Test.MethodReflection.GetMethodCaller<ImplementationDelegate, VeryUseful>("_Implementation");

        // Instance methods of course are also supported
        var useful = new VeryUseful();
        var doStuff = Ockham.Test.MethodReflection.GetMethodCaller<DoStuff, VeryUseful>(useful);
    }
}

The docs provide more complete examples.