Add initial property-based tests using Hypothesis (#22280)

* BLD: Add Hypothesis to build system * TST: Add Hypothesis tests for ticks, offsets These tests are derived from GH18761, by jbrockmendel Co-authored-by: jbrockmendel <jbrockmendel@users.noreply.github.com> * DOC: Explain Hypothesis in contributing guide * TST: remove pointless loop * TST: Improve integration of Hypothesis Responding to review from jreback on GH22280. * Final review fixes

Author: Zac-HD

.gitignore

@@ -62,6 +62,8 @@ dist
 coverage.xml
 coverage_html_report
 *.pytest_cache
+# hypothesis test database
+.hypothesis/
 
 # OS generated files #
 ######################

ci/appveyor-27.yaml

@@ -28,3 +28,4 @@ dependencies:
  - pytest
  - pytest-xdist
  - moto
+ - hypothesis>=3.58.0

ci/appveyor-36.yaml

@@ -25,3 +25,4 @@ dependencies:
  - cython>=0.28.2
  - pytest
  - pytest-xdist
+ - hypothesis>=3.58.0

ci/check_imports.py

@@ -9,6 +9,7 @@
  'html5lib',
  'ipython',
  'jinja2'
+ 'hypothesis',
  'lxml',
  'numexpr',
  'openpyxl',

ci/circle-27-compat.yaml

@@ -26,3 +26,4 @@ dependencies:
  - html5lib==1.0b2
  - beautifulsoup4==4.2.1
  - pymysql==0.6.0
+ - hypothesis>=3.58.0

ci/circle-35-ascii.yaml

@@ -11,3 +11,5 @@ dependencies:
  # universal
  - pytest
  - pytest-xdist
+ - pip:
+ - hypothesis>=3.58.0

ci/circle-36-locale.yaml

@@ -31,3 +31,5 @@ dependencies:
  - pytest
  - pytest-xdist
  - moto
+ - pip:
+ - hypothesis>=3.58.0

ci/circle-36-locale_slow.yaml

@@ -32,3 +32,5 @@ dependencies:
  - pytest
  - pytest-xdist
  - moto
+ - pip:
+ - hypothesis>=3.58.0

ci/environment-dev.yaml

@@ -7,6 +7,7 @@ dependencies:
  - NumPy
  - flake8
  - flake8-comprehensions
+ - hypothesis>=3.58.0
  - moto
  - pytest>=3.6
  - python-dateutil>=2.5.0

ci/requirements_dev.txt

@@ -4,6 +4,7 @@ Cython>=0.28.2
 NumPy
 flake8
 flake8-comprehensions
+hypothesis>=3.58.0
 moto
 pytest>=3.6
 python-dateutil>=2.5.0