Lazy tests: parse using regex first

[elazarg]

Fix #1073: parse tests on collection only enough to find the name, so small number of tests run faster

On my machine, pytest -n0 -k testAttrsSimple takes at least 2.24 seconds to finish on master, and at most 0.95 seconds to finish with this PR.

• 'skip-cache' is changed to 'only_when_nocache' and similarly 'skip-nocache'
• I have replace while loops with "if True" to make the diff simpler. Further cleanup and optimizations are also possible

[msullivan]

Sorry for the big delay in reviewing this.

The speedups for running single tests will be really nice and I am happy with the approach here.

Could you go ahead and get rid of the if Trues and then we can merge this?

[elazarg]

Additional refactoring and cleanup:

• rename variables to be consistent and clear (e.g. test_items instead of p)
• extract variables and switch to for-loop
• combine the out cases, removing repetition
• rechecked/stale cases reformatted so the repetition is obvious
• fail faster in case out_section_missing, with a clearer error message

[elazarg]

Linux 3.4 / 3.5.1 seem to fail spuriously - "Unable to download 3.5.1 archive"?

(The windows tests fail due to path separator on the expected output being reversed when it shouldn't)

[msullivan]

I've restarted the linux builds

[msullivan]

Thank you!

[gvanrossum]

Since this PR landed, pytest -v mypy/test/testcheck.py prints a stream of messages like this:

[location] PASSED                   [  0%]
[location] PASSED                   [  0%]
[location] PASSED                   [  0%]

Previously it would print the test name instead of the string [location], e.g.:

mypy/test/testcheck.py::TypeCheckSuite::testEmptyFile <- /Users/guido/src/mypy-master/test-data/unit/check-basic.test PASSED                                              [  0%]
mypy/test/testcheck.py::TypeCheckSuite::testAssignmentAndVarDef <- /Users/guido/src/mypy-master/test-data/unit/check-basic.test PASSED                                    [  0%]
mypy/test/testcheck.py::TypeCheckSuite::testConstructionAndAssignment <- /Users/guido/src/mypy-master/test-data/unit/check-basic.test PASSED                              [  0%]

Methinks something went wrong here. @elazarg do you have a hunch as to what caused this? (I feel I've done enough research by bisecting it to this PR.)

[elazarg]

Of course. Sorry!