I love Typemock Isolator. I do. The power it gives me to deal with legacy code interaction testing is phenomenal.

However, every once in a while, I'll get an odd failure that doesn't make sense. Today's error message looks like this:

SetUp method failed. SetUp : TypeMock.ArrangeActAssert.NestedCallException : 
*** WhenCalled does not support using a property call as an argument.
-   To fix this pass null instead of LoggerWrapperImpl.Logger

***
* Example - this would work:
-   MyObj argument = Something.Other().GetStuff();
-   Isolate.WhenCalled(() => ObjUnderTest.MethodUnderTest(argument))...;
***
* Example - this would not work:
-   Isolate.WhenCalled(() => ObjUnderTest.MethodUnderTest(Something.Other().GetStuff()))...;
at cv.a()
at hg.a()
at dj.a(Boolean A_0)
at do.b(Boolean A_0)
at iz.b(Boolean A_0)
at iz.a(Object A_0, Boolean A_1, Func`1 A_2, Action A_3, Action A_4, Action A_5)
at iz.b(Object A_0)
...

We weren't doing anything odd in the test that failed, and we have other tests that do very similar stuff. What gives?

Doing a little poking around in the TeamCity build logs, I found that the failing test...

• Was the first one to run in the given test assembly, and
• The test fixture setup had a call to mock a static method on a static class.

Which means static construction wasn't happening on the static class and was causing some weird problems.

I fixed the issue by adding a real call to a static method on the class – just enough to get static construction to run first. Then everything worked perfectly.

Why did it pass on my dev box and not on the build box? Tests were getting run in a different order. Static construction was happening on the class in a different test.

Like I said, I love Typemock, but sometimes... sometimes there are some gotchas.