Report error when attempting prerequisite for private function

[gregspurrier]

I took a stab at adding the error message discussed in Issue #140. Please let me know if there is a better way to approach this.

The test run now looks like:

% lein midje

FAIL at (foobar/test/core.clj:14)
    Midje could not understand something you wrote: 
        Prerequisites cannot be specified for private functions exposed with expose-testables.
FAILURE: 1 fact was not confirmed. (But 1 was.)

I'd be happy to add a corresponding test in test/midje/test/t_semi_sweet_validations.clj. Do you have any suggestions for where to put a private function for testing? Or should I test against an existing one?

[gregspurrier]

BTW, I'm planning on adding some metadata to the var created by expose-testables so that the original namespace will be available when generating the error message. That way we can give a helpful suggestion like "Instead refer to the private var directly. E.g.,: #'foo.core/private-function".

[gregspurrier]

I improved the error message to make it more helpful. I didn't need to modify expose-testables after all. The metadata already had the namespace.

Here's the new output:

% lein midje

FAIL at (foobar/test/core.clj:14)
    Midje could not understand something you wrote: 
        A prerequisite cannot be specified on a function exposed via expose-testables.
        Instead, specify it directly on the var: #'foobar.core/private-function
FAILURE: 1 fact was not confirmed. (But 1 was.)