Adds a unit test scaffolding

.gitignore

@@ -1,2 +1,4 @@
 .DS_Store
-vendor
+node_modules
+vendor
+.phpunit.result.cache

.phpcs.xml.dist

@@ -0,0 +1,47 @@
+<?xml version="1.0"?>
+<ruleset name="WordPress Coding Standards based custom ruleset for your plugin">
+	<description>Generally-applicable sniffs for WordPress plugins.</description>
+
+	<!-- What to scan -->
+	<file>.</file>
+	<exclude-pattern>/vendor/</exclude-pattern>
+	<exclude-pattern>/node_modules/</exclude-pattern>
+
+	<!-- How to scan -->
+	<!-- Usage instructions: https://github.com/squizlabs/PHP_CodeSniffer/wiki/Usage -->
+	<!-- Annotated ruleset: https://github.com/squizlabs/PHP_CodeSniffer/wiki/Annotated-ruleset.xml -->
+	<arg value="sp"/> <!-- Show sniff and progress -->
+	<arg name="basepath" value="./"/><!-- Strip the file paths down to the relevant bit -->
+	<arg name="colors"/>
+	<arg name="extensions" value="php"/>
+	<arg name="parallel" value="8"/><!-- Enables parallel processing when available for faster results. -->
+
+	<!-- Rules: Check PHP version compatibility -->
+	<!-- https://github.com/PHPCompatibility/PHPCompatibility#sniffing-your-code-for-compatibility-with-specific-php-versions -->
+	<config name="testVersion" value="5.6-"/>
+	<!-- https://github.com/PHPCompatibility/PHPCompatibilityWP -->
+	<rule ref="PHPCompatibilityWP"/>
+
+	<!-- Rules: WordPress Coding Standards -->
+	<!-- https://github.com/WordPress-Coding-Standards/WordPress-Coding-Standards -->
+	<!-- https://github.com/WordPress-Coding-Standards/WordPress-Coding-Standards/wiki/Customizable-sniff-properties -->
+	<config name="minimum_supported_wp_version" value="4.6"/>
+	<rule ref="WordPress"/>
+	<rule ref="WordPress.NamingConventions.PrefixAllGlobals">
+		<properties>
+			<!-- Value: replace the function, class, and variable prefixes used. Separate multiple prefixes with a comma. -->
+			<property name="prefixes" type="array" value="my-plugin"/>
+		</properties>
+	</rule>
+	<rule ref="WordPress.WP.I18n">
+		<properties>
+			<!-- Value: replace the text domain used. -->
+			<property name="text_domain" type="array" value="my-plugin"/>
+		</properties>
+	</rule>
+	<rule ref="WordPress.WhiteSpace.ControlStructureSpacing">
+		<properties>
+			<property name="blank_line_check" value="true"/>
+		</properties>
+	</rule>
+</ruleset>

.travis.yml

@@ -0,0 +1,71 @@
+sudo: false
+dist: trusty
+
+language: php
+
+notifications:
+  email:
+    on_success: never
+    on_failure: change
+
+branches:
+  only:
+    - master
+
+cache:
+  directories:
+    - $HOME/.composer/cache
+
+matrix:
+  include:
+    - php: 7.4
+      env: WP_VERSION=latest
+    - php: 7.3
+      env: WP_VERSION=latest
+    - php: 7.2
+      env: WP_VERSION=latest
+    - php: 7.1
+      env: WP_VERSION=latest
+    - php: 7.0
+      env: WP_VERSION=latest
+    - php: 5.6
+      env: WP_VERSION=4.0.0
+    - php: 5.6
+      env: WP_VERSION=latest
+    - php: 5.6
+      env: WP_VERSION=trunk
+    - php: 5.6
+      env: WP_TRAVISCI=phpcs
+
+before_script:
+  - export PATH="$HOME/.composer/vendor/bin:$PATH"
+  - |
+    if [ -f ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/xdebug.ini ]; then
+      phpenv config-rm xdebug.ini
+    else
+      echo "xdebug.ini does not exist"
+    fi
+  - |
+    if [[ ! -z "$WP_VERSION" ]] ; then
+      bash bin/install-wp-tests.sh wordpress_test root '' localhost $WP_VERSION
+      composer global require "phpunit/phpunit=4.8.*|5.7.*"
+    fi
+  - |
+    if [[ "$WP_TRAVISCI" == "phpcs" ]] ; then
+      composer global require wp-coding-standards/wpcs
+      composer global require phpcompatibility/php-compatibility
+      composer global require phpcompatibility/phpcompatibility-paragonie
+      composer global require phpcompatibility/phpcompatibility-wp
+      phpcs --config-set installed_paths $HOME/.composer/vendor/wp-coding-standards/wpcs,$HOME/.composer/vendor/phpcompatibility/php-compatibility,$HOME/.composer/vendor/phpcompatibility/phpcompatibility-paragonie,$HOME/.composer/vendor/phpcompatibility/phpcompatibility-wp
+    fi
+
+script:
+  - |
+    if [[ ! -z "$WP_VERSION" ]] ; then
+      phpunit
+      WP_MULTISITE=1 phpunit
+    fi
+  - |
+    if [[ "$WP_TRAVISCI" == "phpcs" ]] ; then
+      phpcs
+    fi

.wp-env.json

@@ -0,0 +1,9 @@
+{
+    "core": "WordPress/WordPress",
+    "plugins": [ "." ],
+    "env": {
+        "tests": {
+            "phpVersion": "8.1"
+        }
+    }
+}

composer.json

@@ -21,9 +21,10 @@
         "dealerdirect/phpcodesniffer-composer-installer": "*",
         "object-calisthenics/phpcs-calisthenics-rules": "*",
         "phpcompatibility/php-compatibility": "*",
-        "wp-coding-standards/wpcs": "*"
+        "wp-coding-standards/wpcs": "*",
+        "phpunit/phpunit": "^8",
+        "yoast/phpunit-polyfills": "^2.0"
     },
-    "require": {},
     "config": {
         "allow-plugins": {
             "dealerdirect/phpcodesniffer-composer-installer": true,