* Fixes the "Installing <version>" assertions so that they don't false
positive against the "please upgrade to <version>" output.
* Removes modification of test fixtures during tests, since it can lead
to failures depending on test order, and confusion when debugging.
* Updates the PyPy version warning tests to use a slightly newer (but
still not latest) PyPy version, which means that the test now passes
on Cedar-14 and can be unskipped.
* Switches to using an empty requirements file for version tests that
duplicate the main test, to save spending time installing dependencies
unnecessarily.
* Switches the NLTK test to using the default buildpack Python version,
rather than an ancient Python 3.6.
* Skips the Python 3.7/3.8 tests on Cedar-14 rather than asserting
failure, since we know they'll never pass due to Cedar-14's libssl being
older than required.
* Removes redundant `testSqliteInstall` test since it duplicates the
Python version install tests.
Longer term I'll be moving many of the unit tests to Hatchet, however
this at least makes the tests more dependable in the meantime.
Closes @W-8060219@.
Closes @W-8176779@.
[skip changelog]
Ed Morley