Refactoring specs to remove warning

[jeremyf]

Adjusting method PluggableDerivativeService implementation

e7e0675

Prior to this commit, the respond_to_missing? method definition did
not have the correct method signature. Which could cause failures
elsewhere.

Also, as much as we don't want to repeat knowledge regarding
implementation details, most references to method_missing and the
sibling respond_to_missing duplicate logic; in part to minimize
unnecessary calls. (See Always Define respond_to_missing?)

I renamed name to method_name to be consistent with the
parameters of the sibling methods.

And last, I made a change in the logic test to short-circuit faster and
not reference the file_set if we don't have "agreeable" parameters.

References:

• Clean up specs #43

Removing RSpec matcher warning

ba0268f

Prior to this commit the specs included the following warning:

WARNING: Using expect { }.not_to raise_error(SpecificErrorClass)
risks false positives, since literally any other error would cause the
expectation to pass, including those raised by Ruby
(e.g. NoMethodError, NameError and ArgumentError), meaning the
code you are intending to test may not even get reached. Instead
consider using expect { }.not_to raise_error or expect { }.to raise_error(DifferentSpecificErrorClass).

With this commit, we're removing that warning.

Less warnings, means less chatter.

Related to:

• Clean up specs #43