private void FailUnexpectedInvocation(Invocation invocation)
{
var description = new StringDescriptionWriter();
description.AppendText("unexpected invocation of ");
invocation.DescribeOn(description);
description.AppendNewLine();
DescribeActiveExpectationsTo(description);
description.AppendList("\nstates:\n" , Environment.NewLine, string.Empty, stateMachines);
// try catch to get exception with stack trace.
throw new ExpectationException(description.ToString());
}
