Tests: Adds unit-tests for models (#1287)

This adds model tests to BookablePost, Booking, Week, Calendar, Location and Timeframe model classes.

For this it introduces the clock-mock library, to ease the testing of time-dependent code. clock-mock needs the uopz php extension.

Several small fixes:

* Fixes missing grid variable after refactoring
* Fixes method invocation of commented test
* Refactors the bookingLink invocation
* Fixes CB::get invocation with missing post value
---------

Co-authored-by: Hans Morbach <6433480+hansmorb@users.noreply.github.com>

.github/workflows/php.yml

@@ -29,6 +29,7 @@ jobs:
     - uses: shivammathur/setup-php@v2
       with:
         php-version: '7.4'
+        extensions: uopz
 
     - name: Validate composer.json and composer.lock
       run: composer validate

composer.json

@@ -3,8 +3,11 @@
   "description": "~",
   "version": "0.0.1",
   "config": {
-    "platform-check": false
-    },
+    "platform-check": false,
+    "allow-plugins": {
+      "php-http/discovery": true
+    }
+  },
   "autoload": {
     "files": [
       "includes/OptionsArray.php",
@@ -13,7 +16,9 @@
       "includes/TemplateParser.php",
       "includes/Users.php"
     ],
-    "psr-4": {"CommonsBooking\\": "src/"}
+    "psr-4": {
+      "CommonsBooking\\": "src/"
+    }
   },
   "autoload-dev": {
     "psr-4": {
@@ -44,7 +49,8 @@
   "require-dev": {
     "mockery/mockery": "1.*",
     "phpunit/phpunit": "7.*",
-    "yoast/phpunit-polyfills": "^1.0",
-    "wp-coding-standards/wpcs": "^2.3"
+    "slope-it/clock-mock": "^0.3.8",
+    "wp-coding-standards/wpcs": "^2.3",
+    "yoast/phpunit-polyfills": "^1.0"
   }
 }