Make the test suite run faster

[thiagoa]

In favor of a better development experience, make Suspender's test suite run faster. It takes around 35 minutes in CI to run the full test suite and it takes even more on a local machine, so developers are generally discouraged to run it while developing.

Most generators are being tested end-to-end with expensive network calls (Bundler) and rails generate commands. However, it is possible to run the generator's code alone within the same process as RSpec.

Here's a preliminary idea:

• Test generator classes separately
  • For every generator spec, use a fake Rails project directory
  • Stub out any network calls and stdout output
  • After the generator test has enough coverage, delete the equivalent end-to-end spec
  • Create custom matchers if necessary to make the generator specs more readable and efficient
• Have fewer end-to-end specs with more assertions. If possible, run many generators at once in a single spec.

In any case, we must ensure coverage does not drop and that we test what needs to be tested.

[thiagoa]

We've now made existing generator tests leaner, so I'm closing this ticket. For any other improvements to the test suite we can open new tickets, but I think this work will naturally evolve as we extract new generators from 'AppGenerator'.