Test added hooks

With Brain Monkey there are two ways to test some hook have been added, and with which arguments.
First method (easier) makes use of WordPress functions, the second (more powerful) makes use of Brain Monkey (Mockery) expectation DSL.
Testing framework agnostic
Brain Monkey can be used with any testing framework. Examples in this page will use PHPUnit, but the concepts are applicable to any testing framework.
Also note that test classes in this page extends the class MyTestCase that is assumed very similar to the one coded in the WordPress / Setup docs section.
Testing with WordPress functions: has_action() and has_filter()
When Brain Monkey is loaded for tests it registers all the functions of WordPress plugin API (see WordPress / WordPress Testing Tools). Among them there are has_action() and has_filter() that, just like real WordPress functions can be used to test if some hook (action or filter) has been added, and also verify the arguments.
Let's assume the code to be tested is:
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namespace Some\Name\Space;
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​
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class MyClass {
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​
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    public function addHooks() {
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​
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       add_action('init', [__CLASS__, 'init'], 20);
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       add_filter('the_title', [__CLASS__, 'the_title'], 99);
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    }
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}
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in Brain Monkey, just like in real WordPress code, you can test hooks are added using WordPress functions:
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use Some\Name\Space\MyClass;
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​
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class MyClassTest extends MyTestCase {
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​
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  public function testAddHooksActuallyAddsHooks() {
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​
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        ( new MyClass() )->addHooks();
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        self::assertNotFalse( has_action('init', [ MyClass::class, 'init' ]) );
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        self::assertNotFalse( has_filter('the_title', [ MyClass::class, 'the_title' ] ) );
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    }
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}
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Nice thing of this approach is that you don't need to remember Brain Monkey classes and methods names, you can just use functions you, as a WordPress developer, are already used to use.
There's more.
A problem of WordPress hooks is that when dynamic object methods or anonymous functions are used, identify them is not easy. It's pretty hard, to be honest.
But Brain Monkey is not WordPress, and it makes these sort of things very easy. Let's assume the code to test is:
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namespace Some\Name\Space; 
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​
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class MyClass {
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​
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    public function init() {
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      /* ... */
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    }
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​
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    public function addHooks() {
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       add_action('init', [ $this, 'init' ], 20);
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    }
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}
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Using real WordPress functions, to check hooks added like in code above is pretty hard, because we don't have access to $this outside of the class.
But Brain Monkey version of has_action and has_filter allow to check this cases with a very intuitive syntax:
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class MyClassTest extends MyTestCase
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{
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    public function testAddHooksActuallyAddsHooks()
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    {
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        $class = new \Some\Name\Space\MyClass\MyClass();
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        $class->addHooks();
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​
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        self::assertSame( 20, has_action( 'init', 'Some\Name\Space\MyClass->init()' ) );
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    }
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}
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So we have identified a dynamic method by using the class name, followed by -> and the method name followed by parenthesis.
Moreover
a static method can be identified by the class name followed by :: and the method name followed by parenthesis, e.g. 'Some\Name\Space\MyClass::init()'
an invokable object (a class with a __invoke() method) can be identified by the class name followed by parenthesis, e.g. 'Some\Name\Space\MyClass()'
Note that fully qualified names of classes are used and namespace.
Identify Closures
One tricky thing when working with hooks and closures in WordPress is that they are hard to identify, for example to remove or even to check via has_action() / has_filter() if a specific closure has been added to an hook.
Brain Monkey makes this a bit easier thanks to a sort of "serialization" of closures: a closure can be identified by a string very similar to the PHP code used to define the closure. Hopefully, an example will make it more clear.
Assuming a code like:
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namespace Some\Name\Space; 
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​
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class MyClass {
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​
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  public function addHooks() {
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​
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       add_filter('the_title', function($title) {
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          return $title;
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       }, 99);
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    }
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}
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It could be tested with:
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class MyClassTest extends MyTestCase
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{
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    public function testAddHooksActuallyAddsHooks()
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    {
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        $class = new \Some\Name\Space\MyClass();
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        $class->addHooks();
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​
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        self::assertNotFalse( has_filter('the_title', 'function ($title)' ) );
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    }
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}
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It also works with type-hints and variadic arguments. E.g. a closure like:
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namespace Foo\Bar;
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​
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function( array $foo, Baz $baz, Bar ...$bar) {
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  // ....
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}
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could be identified like this:
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'function ( array $foo, Foo\Bar\Baz $baz, Foo\Bar\Bar ...$bar )';
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Just note how classes used in type-hints were using relative namespace on declaration, always need the fully qualified name in the closure string representation.
PHP 7+ scalar type hints are perfectly supported.
The serialization also recognizes static closures. Following closure:
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static function( int $foo, Bar ...$bar ) {
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  // ....
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}
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could be identified like this:
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'static function ( int $foo, Bar ...$bar )';
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Things that are not took into account during serialization:
default values for arguments
PHP 7+ return type declarations
For example all following closures:
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function( array $foo, $bar ) {
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  // ....
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}
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​
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function( array $foo = [], $bar = null ) {
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  // ....
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}
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​
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function( array $foo, $bar ) : array {
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  // ....
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}
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​
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function( array $foo, $bar = null ) : array {
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  // ....
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}
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are serialized into :
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'function ( array $foo, $bar )';
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Testing with expectations
Even if the doing tests using WordPress native functions is pretty easy, there are cases in which is not enough powerful, or the expectation methods are just more convenient.
Moreover, Brain Monkey functions always try to mimic WordPress real functions behavior and so a call to remove_action or remove_filter can make impossible to test some code using has_action and has_filter, because hooks are actually removed.
The solution is to use expectations, provided in Brain Monkey by Mockery.
Assuming the class to test is:
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namespace Some\Name\Space; 
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​
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class MyClass {
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​
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  public function addHooks() {
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​
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       add_action('init', [$this, 'init']);
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​
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       add_filter('the_title', function($title) {
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          return $title;
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       }, 99);
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    }
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}
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it can be tested like so:
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use Brain\Monkey\Actions;
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use Brain\Monkey\Filters;
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​
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class MyClassTest extends MyTestCase
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{
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    function testAddHooksActuallyAddsHooks()
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    {
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        Actions\expectAdded('init');
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​
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        Filters\expectAdded('the_title')->with(\Mockery::type('Closure'));
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​
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        // let's use the code that have to satisfy our expectations
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       ( new \Some\Name\Space\MyClass() )->addHooks();
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    }
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}
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This is just an example, but Mockery expectations are a very powerful testing mechanism.
To know more, read Mockery documentation, and have a look to PHP Functions doc section to see how it is used seamlessly in Brain Monkey.
Just a couple of things...
expectations must be set before the code to be tested runs: they are called "expectations" for a reason;
argument validation done using with(), validates hook arguments, not function arguments, it means what is passed to add_action() or add_filter() excluding hook name itself.
If you are errors related to Call to undefined function add_action() it could have to do with how you are loading your plugin file in the bootstrap.php file. See some tips for procedural/OOP setup.
Don't set expectations on return values for added hooks
Maybe you already know that add_action() and add_filter() always return true.
As already said, Brain Monkey always tries to make WordPress functions behave how they do in real WordPress code, for this reason Brain Monkey version of those functions returns true as well.
But if you read PHP Functions doc section or Mockery documentation you probably noticed a andReturn method that allows to force an expectation to return a given value.
Once expectAdded() method works with Mockery expectations, you may be tempted to use it... if you do that an exception will be thrown.
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// this expectation will thrown an error!
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Filters\expectAdded('the_title')->once()->andReturn(false);
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Reason is that if Brain Monkey had allowed a mocked returning value for add_action and add_filter that had been in contrast with real WordPress code, with disastrous effects on tests.
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Setup for WordPress testing
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Test done hooks
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Contents
Testing framework agnostic
Testing with WordPress functions: has_action() and has_filter()
Identify Closures
Testing with expectations
Just a couple of things...
Don't set expectations on return values for added hooks