Hypothesis health checks don't pass reliably if "CI" is not set in the environment. #132

$ tox -e py36
GLOB sdist-make: /tmp/hyperlink/setup.py
py36 create: /tmp/hyperlink/.tox/py36
py36 installdeps: idna==2.9, pytest==5.2.4, coverage==4.5.4, pytest-cov==2.10.0, hypothesis==5.8.6
py36 inst: /tmp/hyperlink/.tox/.tmp/package/1/hyperlink-20.0.1.dev0.zip
py36 installed: atomicwrites==1.4.0,attrs==19.3.0,coverage==4.5.4,hyperlink @ file:///tmp/hyperlink/.tox/.tmp/package/1/hyperlink-20.0.1.dev0.zip,hypothesis==5.8.6,idna==2.9,importlib-metadata==1.7.0,more-itertools==8.4.0,packaging==20.4,pluggy==0.13.1,py==1.9.0,pyparsing==2.4.7,pytest==5.2.4,pytest-cov==2.10.0,six==1.15.0,sortedcontainers==2.2.2,wcwidth==0.2.5,zipp==3.1.0
py36 run-test-pre: PYTHONHASHSEED='2292208485'
py36 run-test: commands[0] | pytest --cov=hyperlink --cov-report=term-missing:skip-covered --doctest-modules src/hyperlink
=============================================================== test session starts ===============================================================
platform linux -- Python 3.6.11, pytest-5.2.4, py-1.9.0, pluggy-0.13.1
cachedir: .tox/py36/.pytest_cache
rootdir: /tmp/hyperlink, inifile: pytest.ini
plugins: hypothesis-5.8.6, cov-2.10.0
collected 130 items                                                                                                                               

src/hyperlink/_url.py ....................                                                                                                  [ 15%]
src/hyperlink/test/test_common.py ......                                                                                                    [ 20%]
src/hyperlink/test/test_decoded_url.py ..........                                                                                           [ 27%]
src/hyperlink/test/test_hypothesis.py ......F.......                                                                                        [ 38%]
src/hyperlink/test/test_parse.py .                                                                                                          [ 39%]
src/hyperlink/test/test_scheme_registration.py ......                                                                                       [ 43%]
src/hyperlink/test/test_url.py .........................................................................                                    [100%]

==================================================================== FAILURES =====================================================================
______________________________________________ TestHypothesisStrategies.test_hostnames_ascii_nolead _______________________________________________

self = <hyperlink.test.test_hypothesis.TestHypothesisStrategies testMethod=test_hostnames_ascii_nolead>

    @given(hostnames(allow_leading_digit=False, allow_idn=False))
>   def test_hostnames_ascii_nolead(self, hostname):
        # type: (Text) -> None
        """
        hostnames(allow_leading_digit=False, allow_idn=False) generates
        ASCII host names without leading digits.
E       hypothesis.errors.FailedHealthCheck: Data generation is extremely slow: Only produced 1 valid examples in 1.01 seconds (40 invalid ones and 0 exceeded maximum size). Try decreasing size of the data you're generating (with e.g.max_size or max_leaves parameters).
E       See https://hypothesis.readthedocs.io/en/latest/healthchecks.html for more information about this. If you want to disable just this health check, add HealthCheck.too_slow to the suppress_health_check settings for this test.

src/hyperlink/test/test_hypothesis.py:177: FailedHealthCheck
------------------------------------------------------------------- Hypothesis --------------------------------------------------------------------
You can add @seed(2426485286323854916506411185325111964) to this test or run pytest with --hypothesis-seed=2426485286323854916506411185325111964 to reproduce this failure.

---------- coverage: platform linux, python 3.6.11-final-0 -----------
Name                                    Stmts   Miss Branch BrPart  Cover   Missing
-----------------------------------------------------------------------------------
src/hyperlink/_socket.py                   22     20      2      0     8%   3-53
src/hyperlink/_url.py                     690     21    349     12    96%   28-29, 52-53, 115, 122, 126, 253, 280, 378, 391, 571, 886-887, 1201, 1822-1823, 1845-1847, 2370-2372, 113->115, 195->197, 250->253, 277->280, 375->378, 388->391, 570->571, 884->886, 1200->1201, 1519->1524, 1821->1822, 2274->exit
src/hyperlink/hypothesis.py               111      5     37      2    95%   11-14, 101, 244, 100->101, 243->244
src/hyperlink/test/__init__.py             12      6      2      1    50%   14-28, 13->14
src/hyperlink/test/test_hypothesis.py      72      4      6      0    95%   10-11, 18-19
src/hyperlink/test/test_socket.py          29     26      4      1    12%   5-6, 9-45, 8->9
src/hyperlink/test/test_url.py            579      3     16      1    99%   940, 1472-1473, 1471->1472
-----------------------------------------------------------------------------------
TOTAL                                    1766     85    422     17    95%

6 files skipped due to complete coverage.

========================================================= 1 failed, 129 passed in 59.10s ==========================================================
ERROR: InvocationError for command /tmp/hyperlink/.tox/py36/bin/pytest --cov=hyperlink --cov-report=term-missing:skip-covered --doctest-modules src/hyperlink (exited with code 1)
_____________________________________________________________________ summary _____________________________________________________________________
ERROR:   py36: commands failed