How would I get full OpenCover branch coverage for these code examples?

Question

I want to test the following two (unrelated) methods and achieve full branch and statement coverage using OpenCover 2.0.802.1

public class Methods
{
    public static void MethodWithDelegate(SynchronizationContext context)
    {
        context.Send(delegate { Console.Beep(); }, null);
    }

    public static string MethodWithSwitchStatement(Type value)
    {
        string output = string.Empty;

        if (value != null)
        {
            switch (value.ToString())
            {
                case "System.Int32":
                    output = "int";
                    break;
                default:
                    output = "other type";
                    break;
            }
        }

        return output;
    }
}

I have written the following (NUnit) tests, one using a 'Moq' mock object:

[Test]
public void Test_ShouldCoverMethodWithDelegate()
{
    var context = new Mock<SynchronizationContext>();

    Methods.MethodWithDelegate(context.Object);

    context.Verify(x => x.Send(It.IsAny<SendOrPostCallback>(), It.IsAny<object>()));
}

[Test]
public void Test_ShouldCoverSwitchStatement()
{
    Assert.That(Methods.MethodWithSwitchStatement(null), Is.EqualTo(string.Empty));
    Assert.That(Methods.MethodWithSwitchStatement(typeof(int)), Is.EqualTo("int"));
    Assert.That(Methods.MethodWithSwitchStatement(typeof(float)), Is.EqualTo("other type"));
}

However, after running the tests through OpenCover, the coverage.xml file always contains a branch point with a zero visit count for both tests. The sequence coverage shows 100%.

Not being an IL expert, I'm not sure how I'd go about writing further tests to get the branch coverage to 100%.

Answer 1

Okay first lets look at the first method in IL (I am using IL SPY)

.method public hidebysig static 
void MethodWithDelegate (
    class [mscorlib]System.Threading.SynchronizationContext context
) cil managed 
{
// Method begins at RVA 0x2059
// Code size 41 (0x29)
.maxstack 8

IL_0000: nop
IL_0001: ldarg.0
IL_0002: ldsfld class [mscorlib]System.Threading.SendOrPostCallback so8254847.Methods::'CS$<>9__CachedAnonymousMethodDelegate1'
IL_0007: brtrue.s IL_001c

IL_0009: ldnull
IL_000a: ldftn void so8254847.Methods::'<MethodWithDelegate>b__0'(object)
IL_0010: newobj instance void [mscorlib]System.Threading.SendOrPostCallback::.ctor(object, native int)
IL_0015: stsfld class [mscorlib]System.Threading.SendOrPostCallback so8254847.Methods::'CS$<>9__CachedAnonymousMethodDelegate1'
IL_001a: br.s IL_001c

IL_001c: ldsfld class [mscorlib]System.Threading.SendOrPostCallback so8254847.Methods::'CS$<>9__CachedAnonymousMethodDelegate1'
IL_0021: ldnull
IL_0022: callvirt instance void [mscorlib]System.Threading.SynchronizationContext::Send(class [mscorlib]System.Threading.SendOrPostCallback, object)
IL_0027: nop
IL_0028: ret
} // end of method Methods::MethodWithDelegate

As you can see there is a conditional branch at IL_0007 which only gets executed if the cached anonymous delegate has been set otherwise it goes through the main code of setting up your delegate and then calling it.

SOLUTION: Run the test twice - or forget about it as it is a bit of .NET optimization

Now for the 2nd problem this time it is better to see what was actually produced in C# - you wrote switch statements but the compiler has used ifs instead

public static string MethodWithSwitchStatement(Type value)
{
    string output = string.Empty;
    if (value != null)
    {
        string a;
        if ((a = value.ToString()) != null && a == "System.Int32")
        {
            output = "int";
        }
        else
        {
            output = "other type";
        }
    }
    return output;
}

As you can see the compiler has introduced an if null test with the switch statement but because you already have this already then it will never be executed.

SOLUTION: remove your initial if null test (as it is not needed).