Unit Test for WordPress' save_post{$post_type}

save_post_post_type_test.php

<?php

/**
 * This has been tested using the diff for save_post_{$post_type}
 * https://core.trac.wordpress.org/changeset/25050
 *
 * @todo  Try different post type names
 * @todo  Create two posts and try to update them both at the same time
 */

class Save_Post_Post_Type {

	/**
	 * Loads our control data into the test post.
	 *
	 * First, we'll save the post using wp_update_post and without save_post_{$post_type}
	 * We'll use this as a control to compare our $result against later.
	 * We can't just compare the raw post input with the save_post_{$post_type} because saving
	 * the post strips slashes, validates, etc.
	 *
	 * @param   int     $test_post_id    ID of the post we are testing with.
	 * @return  string  $control_result  content of post saved with wp_update_post
	 */
	function control_test( $test_post_id ) {

		$control_post = array();
		$control_post['ID'] = $test_post_id;
		$control_post['post_type'] = 'book';
		$control_post['post_content'] = "Initial Data.";
		$control_post_id = wp_update_post( $control_post );
		/**
		 * when we save it, it returns a post ID,
		 * so we'll need to get our content back out of the control post.
		 */
		$control_post = get_post( $control_post_id);
		$control_result = $control_post->post_content;
		return $control_result;

	}


	/**
	 * Test to see if save_post_{$post_type} hooks into the saving action correctly.
	 *
	 * @param   int     $test_post_id  ID of the post we are testing with.
	 * @param   string  $input         Input from provider() method.
	 * @return  string  $test_result   Content of post(s) updated with save_post_{$post_type}
	 */
	function test_save_post_post_type( $test_post_id, $input ) {

		//Run the hook that should exist, and attempt to change the data.
		add_action( 'save_post_book', $this->modify_content( $test_post_id, $input ) );

		//Get post content by id
		$result_post = get_post( $test_post_id );
		$test_result = $result_post->post_content;

		return $test_result;

	}

	/**
	 * Save our post with new post_content, on 'save_post_book'
	 *
	 * @param  int     $test_post_id  ID of the post we are testing with.
	 * @param  string  $input         Input from provider() method.
	 * @return void
	 */

	function modify_content( $test_post_id, $input ) {

		/**
		* Attempt to overwrite 'the auto-generated post_content' with $input
		* This will be done on 'save_post_book' in test_save_post_type()
		*/
		$test_post_new_content = array();
		$test_post_new_content ['ID'] = $test_post_id;
		$test_post_new_content['post_content'] = $input;
		wp_update_post( $test_post_new_content );
	}

}


/**
 * Set Up Test
 */

class Tests_Save_Post_Post_Type extends WP_UnitTestCase {

	/**
	 * Establish testing variables
	 *
	 * This information will be passed as the parameter ($input) into our test method in this class.
	 * Note that we use @dataProvider to let test_save_post_post_type know we're using this method
	 * Note also that it returns a multidimentional array (an array within an array).
	 * These values will be passed one at a time into our testing function
	 *
	 * @return  array  Array of input content to test "save_post_{$post_type}"
	 */

	public function provider() {

		return array(
			array( '023983775900' ),
			array( '(*&@#)*)&*#@*~_)*?(#' ),
			array( 'http://wordpress.org' ),
			array( 'It\'s a trap!' ),
			array( 'These aren\'t the droids you are looking for.' ),
			array( 'I find you lack of faith disturbing.' ),
			array( 'Ready are you? What know you of ready?' ),
		);

	}



	/**
	 * Tests to ensure save_post_{$post_type} hooks into save_post correctly.
	 *
	 * If these $input and $result don't match, the test will throw an error.
	 * They should match, displaying that the input matches the output ($result),
	 * when saved by "save_post_{post_type}".
	 *
	 * This function must begin with "test".
	 *
	 * @param  string  $input  Input from provider()
	 * @return bool            Pass/Fail test Results
	 *
	 * The following line is required to let the test know what method is sending the $input
	 * @dataProvider  provider
	 */
	public function test_run_test( $input ) {
		$test = new Save_Post_Post_Type;

		//Create Post using extended class WP_UnitTestCase
		$test_post_id = $this->factory->post->create();

		$control_result = $test->control_test( $test_post_id );

		/**
		 * Run the test.  Send the input, return the result.
		 *
		 * This method changes the content of our post into a Star Wars quote.
		 * If it does not change, it will thow an error.  Remember, our original content was,
		 * "Initial Data."
		 */
		$test_result = $test->test_save_post_post_type( $test_post_id, $input );

		/**
		 * Compare $control_result content with $test_result content.
		 *
		 * Since we attempted to modify the content of the "Book" post, this method "assertFlase"
		 * checks to see that these two statements do not match.
		 * There are many other methods you can use here:
		 * http://phpunit.de/manual/current/en/appendixes.assertions.html
		 */

		$this->assertNotEquals( $control_result, $test_result);

	}

}

Could the test not be made way simpler just with something like this?

<?php
/* ... */
function test_update() (
    /* ... */
    $test_post_id = $this->factory->post->create( array( 'post_type' => 'book' ) );
    $called = false;
    $handler = function () use (&$called) {
        $called = true;
    };
    add_action( 'save_post_book', $handler );
    wp_update_post( array( 'ID' => $test_post_id, 'post_title' => 'updated' ) );
    remove_action( 'save_post_book', $handler );
    $this->assertTrue( $called );

@westonruter Wow. I took your advice and cut this code down to about 1/4 the size before I saw your solution. I've noticed that I have quite the penchant for doing things the long way. Nice work!

BTW, that anonymous function is pretty slick. http://bit.ly/171mbtr