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+# Unit tests
+
+Shaarli uses the [PHPUnit](https://phpunit.de/) test framework; it can be installed with [Composer](https://getcomposer.org/), which is a dependency management tool.
+
+## Install composer
+
+You can either use:
+
+- a system-wide version, e.g. installed through your distro's package manager
+- a local version, downloadable [here](https://getcomposer.org/download/).
+
+```bash
+# for Debian-based distros
+sudo apt install composer
+```
+
+
+## Install Shaarli dev dependencies
+
+```bash
+$ cd /path/to/shaarli
+$ make composer_dependencies_dev
+```
+
+## Install and enable Xdebug to generate PHPUnit coverage reports
+
+
+[Xdebug](http://xdebug.org/docs/install) is a PHP extension which provides debugging and profiling capabilities. Install Xdebug:
+
+```bash
+# for Debian-based distros:
+sudo apt install php-xdebug
+
+# for ArchLinux:
+pacman -S xdebug
+
+# then add the following line to /etc/php/php.ini
+zend_extension=xdebug.so
+```
+
+## Run unit tests
+
+Ensure tests pass successuflly:
+
+```bash
+make test
+# ...
+# OK (36 tests, 65 assertions)
+```
+
+In case of failure the test suite will point you to actual errors and output a summary:
+
+```bash
+make test
+# ...
+# FAILURES!
+# Tests: 36, Assertions: 63, Errors: 1, Failures: 2.
+```
+
+By default, PHPUnit will run all suitable tests found under the `tests` directory. Each test has 3 possible outcomes:
+
+- `.` - success
+- `F` - failure: the test was run but its results are invalid
+    - the code does not behave as expected
+    - dependencies to external elements: globals, session, cache...
+- `E` - error: something went wrong and the tested code has crashed
+    - typos in the code, or in the test code
+    - dependencies to missing external elements
+
+If Xdebug has been installed and activated, two coverage reports will be generated:
+
+- a summary in the console
+- a detailed HTML report with metrics for tested code
+    - to open it in a web browser: `firefox coverage/index.html &`
+
+
+### Executing specific tests
+
+Add a [`@group`](https://phpunit.de/manual/current/en/appendixes.annotations.html#appendixes.annotations.group) annotation in a test class or method comment:
+
+```php
+/**
+ * Netscape bookmark import
+ * @group WIP
+ */
+class BookmarkImportTest extends PHPUnit_Framework_TestCase
+{
+   [...]
+}
+```
+
+To run all tests annotated with `@group WIP`:
+```bash
+$ vendor/bin/phpunit --group WIP tests/
+```
+
+## Running tests inside Docker containers
+
+Unit tests can be run inside [Docker](../Docker.md) containers.
+
+Test Dockerfiles are located under `tests/docker/<distribution>/Dockerfile`, and can be used to build Docker images to run Shaarli test suites under commonLinux environments. Dockerfiles are provided for the following environments:
+
+- [`alpine36`](https://github.com/shaarli/Shaarli/blob/master/tests/docker/alpine36/Dockerfile) - [Alpine Linux 3.6](https://www.alpinelinux.org/downloads/)
+- [`debian8`](https://github.com/shaarli/Shaarli/blob/master/tests/docker/debian8/Dockerfile) - [Debian 8 Jessie](https://www.debian.org/DebianJessie) (oldoldstable)
+- [`debian9`](https://github.com/shaarli/Shaarli/blob/master/tests/docker/debian9/Dockerfile) - [Debian 9 Stretch](https://wiki.debian.org/DebianStretch) (oldstable)
+- [`ubuntu16`](https://github.com/shaarli/Shaarli/blob/master/tests/docker/ubuntu16/Dockerfile) - [Ubuntu 16.04 Xenial Xerus](http://releases.ubuntu.com/16.04/) (old LTS)
+
+Each image provides:
+- a base Linux OS
+- Shaarli PHP dependencies (OS packages)
+- test PHP dependencies (OS packages)
+- Composer
+- Tests that run inside the conatiner using a standard Linux user account (running tests as `root` would bypass permission checks and may hide issues)
+
+Build a test image:
+
+```bash
+# build the Debian 9 Docker image
+cd /path/to/shaarli/tests/docker/debian9
+docker build -t shaarli-test:debian9 .
+```
+
+Run unit tests in a container:
+
+```bash
+cd /path/to/shaarli
+# install/update 3rd-party test dependencies
+composer install --prefer-dist
+# run tests using the freshly built image
+docker run -v $PWD:/shaarli shaarli-test:debian9 docker_test
+# run the full test campaign
+docker run -v $PWD:/shaarli shaarli-test:debian9 docker_all_tests
+```