add test README

test/README.md

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+# TEST
+
+---
+
+## Running test suite
+
+Test suite could be launch with `make` by providing the right target depending what you want to achieve.
+
+Under the hood, `pyenv` test suites use `bats` as a test framework and are run on the host or docker depending of the target provided to make.
+
+
+
+### Targets
+
+- `test`
+  - Run the whole test suite on the local host
+- `test-docker`
+  - Run the whole test suite on docker
+    - Some volumes are used in read-only mode
+- `test-unit`
+  - Run the unit test
+- `test-plugin`
+  - Run the plugin test
+- `test-unit-docker-[BASH_VERSION]`
+  - Run the unit test under **official** bash docker container (alpine/busybox) with the specified bash version if present is in the `Makefile`
+  - Some volumes are used in read-only mode
+- `test-unit-docker-gnu-[BASH_VERSION]`
+  - Run the unit test under **official** bash docker container (alpine/busybox), completed by **GNU Tools**, with the specified bash version if present is in the `Makefile`
+  - Some volumes are used in read-only mode
+- `test-plugin-docker-[BASH_VERSION]`
+  - Run the plugin test under **official** bash docker container (alpine/busybox), completed by **GNU Tools**, with the specified bash version if present is in the `Makefile`
+  - Some volumes are used in read-only mode
+- `test-plugin-docker-gnu-[BASH_VERSION]`
+  - Run the plugin test under **official** bash docker container (alpine/busybox), completed by **GNU Tools**, with the specified bash version if present is in the `Makefile`
+  - Some volumes are used in read-only mode
+
+## Targeting specific test / test file
+
+ By setting some environment variables, it is possible to filtering which test and/or test file who will be tested with bats
+
+- `BATS_FILE_FILTER`
+
+  - Run test only with the specified file
+
+- `BATS_TEST_FILTER`
+  - Run test only who corresponding to the filter provided
+
+
+### Examples
+
+```bash
+    $ BATS_TEST_FILTER=".*installed.*" BATS_FILE_FILTER="build.bats" make test-plugin-docker-gnu-3.2.57
+    build.bats
+     ✓ yaml is installed for python
+     ✓ homebrew is used in Linux if Pyenv is installed with Homebrew
+     ✓ homebrew is not used in Linux if Pyenv is not installed with Homebrew
+    
+    3 tests, 0 failures
+    
+    $ BATS_TEST_FILTER=".*installed.*" BATS_FILE_FILTER="build.bats" make test-plugin
+    build.bats
+     ✓ yaml is installed for python
+     ✓ homebrew is used in Linux if Pyenv is installed with Homebrew
+     ✓ homebrew is not used in Linux if Pyenv is not installed with Homebrew
+    
+    3 tests, 0 failures
+```
+
+
+
+## Writing test
+
+To be reproducible, each test use/should use its own `TMPDIR` .  
+It's achieved by using the environment variable `BATS_TEST_TMPDIR` provided by bats that is automatically deleted at the end of each test. More info [here](https://bats-core.readthedocs.io/en/stable/writing-tests.html#special-variables)
+
+Another variable who could be used to source some file who need to be tested is `BATS_TEST_DIRNAME` who point to the directory in which the bats test file is located.