Do not fail silently when mocking a non-existing method

[bartfeenstra]

When configuring a method that did not previously exist on a mocked class or interface, PHPUnit fails silently; it does not let you know that it ignores your configuration. Instead, it should trigger an error or throw an exception, so some "calling undefined method" errors in the code under test can be prevented.

[whatthejeff]

Thanks for the bug report, @bartfeenstra. This is actually a duplicate of sebastianbergmann/phpunit-mock-objects#12.