Media: Add a unit test for `wp_get_mime_types()`.

Props pbearne.
Fixes #47701.

git-svn-id: https://develop.svn.wordpress.org/trunk@45646 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/functions/wpGetMimeTypes.php

@@ -0,0 +1,30 @@
+<?php
+
+/**
+ * Test wp_get_mime_types().
+ *
+ * @group functions.php
+ */
+class Tests_wp_get_mime_types extends WP_UnitTestCase {
+
+	/**
+	 * @ticket 47701
+	 */
+	public function test_all_mime_match() {
+		$mime_types_start = wp_get_mime_types();
+
+		$this->assertInternalType( 'array', $mime_types_start );
+		$this->assertNotEmpty( $mime_types_start );
+
+		add_filter( 'mime_types', '__return_empty_array' );
+		$mime_types_empty = wp_get_mime_types();
+		$this->assertSame( array(), $mime_types_empty );
+
+		remove_filter( 'mime_types', '__return_empty_array' );
+		$mime_types = wp_get_mime_types();
+		$this->assertInternalType( 'array', $mime_types );
+		$this->assertNotEmpty( $mime_types );
+		// Did it revert to the original after filter remove?
+		$this->assertSame( $mime_types_start, $mime_types );
+	}
+}