Merge pull request #242 from Czaki/before_test

Add CIBW_BEFORE_TEST to customize test environment

docs/options.md

@@ -343,6 +343,34 @@ Platform-specific variants also available:<br/>
 CIBW_TEST_EXTRAS: test,qt
 ```
 
+### `CIBW_BEFORE_TEST` {: #before-test}
+> Execute a shell command before testing each wheel
+
+A shell command to run in **each** test virtual environment, before your wheel is installed and tested. This is useful if you need to install a non pip package, change values of environment variables
+or perform multi step pip installation (e.g. installing `scikit-build` or `cython` before install test package)
+
+
+The active Python binary can be accessed using `python`, and pip with `pip`; `cibuildwheel` makes sure the right version of Python and pip will be executed. `{project}` can be used as a placeholder for the absolute path to the project's root and will be replaced by `cibuildwheel`.
+
+On Linux and macOS, the command is run in a shell, so you can write things like `cmd1 && cmd2`.
+
+Platform-specific variants also available:<br/>
+ `CIBW_BEFORE_TEST_MACOS` | `CIBW_BEFORE_TEST_WINDOWS` | `CIBW_BEFORE_TEST_LINUX`
+
+#### Examples
+```yaml
+# install test dependencies with overwritten environment variables. 
+CIBW_BEFORE_TEST: CC=gcc CXX=g++ pip install -r requirements.txt
+
+# chain commands using &&
+CIBW_BEFORE_TEST : rm -rf ./data/cache && mkdir -p ./data/cache
+
+# install non pip python package 
+CIBW_BEFORE_TEST: cd some_dir; ./configure; make; make install
+
+# install python packages that are required to install test dependencies
+CIBW_BEFORE_TEST: pip install cmake scikit-build
+```
 
 ## Other