diff --git a/tests/phpunit/tests/file.php b/tests/phpunit/tests/file.php
index 8ee3e8de20..3aad09e109 100644
--- a/tests/phpunit/tests/file.php
+++ b/tests/phpunit/tests/file.php
@@ -84,7 +84,7 @@ class Tests_File extends WP_UnitTestCase {
 
 	function test_unique_filename_is_valid() {
 		// make sure it produces a valid, writable, unique filename
-		$filename = wp_unique_filename( $this->dir, rand_str() . '.txt' );
+		$filename = wp_unique_filename( $this->dir, __FUNCTION__ . '.txt' );
 
 		$this->assertTrue( $this->is_unique_writable_file($this->dir, $filename) );
 
@@ -93,7 +93,7 @@ class Tests_File extends WP_UnitTestCase {
 
 	function test_unique_filename_is_unique() {
 		// make sure it produces two unique filenames
-		$name = rand_str();
+		$name = __FUNCTION__;
 
 		$filename1 = wp_unique_filename( $this->dir, $name . '.txt' );
 		$this->assertTrue( $this->is_unique_writable_file($this->dir, $filename1) );
@@ -108,7 +108,7 @@ class Tests_File extends WP_UnitTestCase {
 	}
 
 	function test_unique_filename_is_sanitized() {
-		$name = rand_str();
+		$name = __FUNCTION__;
 		$filename = wp_unique_filename( $this->dir, $name . $this->badchars .  '.txt' );
 
 		// make sure the bad characters were all stripped out
@@ -120,7 +120,7 @@ class Tests_File extends WP_UnitTestCase {
 	}
 
 	function test_unique_filename_with_slashes() {
-		$name = rand_str();
+		$name = __FUNCTION__;
 		// "foo/foo.txt"
 		$filename = wp_unique_filename( $this->dir, $name . '/' . $name .  '.txt' );
 
@@ -133,7 +133,7 @@ class Tests_File extends WP_UnitTestCase {
 	}
 
 	function test_unique_filename_multiple_ext() {
-		$name = rand_str();
+		$name = __FUNCTION__;
 		$filename = wp_unique_filename( $this->dir, $name . '.php.txt' );
 
 		// "foo.php.txt" becomes "foo.php_.txt"
@@ -145,7 +145,7 @@ class Tests_File extends WP_UnitTestCase {
 	}
 
 	function test_unique_filename_no_ext() {
-		$name = rand_str();
+		$name = __FUNCTION__;
 		$filename = wp_unique_filename( $this->dir, $name );
 
 		$this->assertEquals( $name, $filename );
diff --git a/tests/phpunit/tests/filters.php b/tests/phpunit/tests/filters.php
index d2e6ddf0d0..fddcf4aade 100644
--- a/tests/phpunit/tests/filters.php
+++ b/tests/phpunit/tests/filters.php
@@ -9,8 +9,8 @@ class Tests_Filters extends WP_UnitTestCase {
 
 	function test_simple_filter() {
 		$a = new MockAction();
-		$tag = rand_str();
-		$val = rand_str();
+		$tag = __FUNCTION__;
+		$val = __FUNCTION__ . '_val';
 
 		add_filter($tag, array($a, 'filter'));
 		$this->assertEquals($val, apply_filters($tag, $val));
@@ -27,8 +27,8 @@ class Tests_Filters extends WP_UnitTestCase {
 
 	function test_remove_filter() {
 		$a = new MockAction();
-		$tag = rand_str();
-		$val = rand_str();
+		$tag = __FUNCTION__;
+		$val = __FUNCTION__ . '_val';
 
 		add_filter($tag, array($a, 'filter'));
 		$this->assertEquals($val, apply_filters($tag, $val));
@@ -46,8 +46,8 @@ class Tests_Filters extends WP_UnitTestCase {
 	}
 
 	function test_has_filter() {
-			$tag = rand_str();
-			$func = rand_str();
+			$tag  = __FUNCTION__;
+			$func = __FUNCTION__ . '_func';
 
 			$this->assertFalse( has_filter($tag, $func) );
 			$this->assertFalse( has_filter($tag) );
@@ -63,8 +63,8 @@ class Tests_Filters extends WP_UnitTestCase {
 	function test_multiple_filters() {
 		$a1 = new MockAction();
 		$a2 = new MockAction();
-		$tag = rand_str();
-		$val = rand_str();
+		$tag = __FUNCTION__;
+		$val = __FUNCTION__ . '_val';
 
 		// add both filters to the hook
 		add_filter($tag, array($a1, 'filter'));
@@ -79,9 +79,9 @@ class Tests_Filters extends WP_UnitTestCase {
 
 	function test_filter_args_1() {
 		$a = new MockAction();
-		$tag = rand_str();
-		$val = rand_str();
-		$arg1 = rand_str();
+		$tag  = __FUNCTION__;
+		$val  = __FUNCTION__ . '_val';
+		$arg1 = __FUNCTION__ . '_arg1';
 
 		add_filter($tag, array($a, 'filter'), 10, 2);
 		// call the filter with a single argument
@@ -95,10 +95,10 @@ class Tests_Filters extends WP_UnitTestCase {
 	function test_filter_args_2() {
 		$a1 = new MockAction();
 		$a2 = new MockAction();
-		$tag = rand_str();
-		$val = rand_str();
-		$arg1 = rand_str();
-		$arg2 = rand_str();
+		$tag  = __FUNCTION__;
+		$val  = __FUNCTION__ . '_val';
+		$arg1 = __FUNCTION__ . '_arg1';
+		$arg2 = __FUNCTION__ . '_arg2';
 
 		// a1 accepts two arguments, a2 doesn't
 		add_filter($tag, array($a1, 'filter'), 10, 3);
@@ -119,8 +119,8 @@ class Tests_Filters extends WP_UnitTestCase {
 
 	function test_filter_priority() {
 		$a = new MockAction();
-		$tag = rand_str();
-		$val = rand_str();
+		$tag = __FUNCTION__;
+		$val = __FUNCTION__ . '_val';
 
 		// make two filters with different priorities
 		add_filter($tag, array($a, 'filter'), 10);
@@ -150,9 +150,9 @@ class Tests_Filters extends WP_UnitTestCase {
 
 	function test_all_filter() {
 		$a = new MockAction();
-		$tag1 = rand_str();
-		$tag2 = rand_str();
-		$val = rand_str();
+		$tag1 = __FUNCTION__ . '_1';
+		$tag2 = __FUNCTION__ . '_2';
+		$val  = __FUNCTION__ . '_val';
 
 		// add an 'all' filter
 		add_filter('all', array($a, 'filterall'));
@@ -174,8 +174,8 @@ class Tests_Filters extends WP_UnitTestCase {
 
 	function test_remove_all_filter() {
 		$a = new MockAction();
-		$tag = rand_str();
-		$val = rand_str();
+		$tag = __FUNCTION__;
+		$val = __FUNCTION__ . '_val';
 
 		add_filter('all', array($a, 'filterall'));
 		$this->assertTrue( has_filter('all') );
@@ -201,8 +201,8 @@ class Tests_Filters extends WP_UnitTestCase {
 	 */
 	function test_remove_all_filters_should_respect_the_priority_argument() {
 		$a = new MockAction();
-		$tag = rand_str();
-		$val = rand_str();
+		$tag = __FUNCTION__;
+		$val = __FUNCTION__ . '_val';
 
 		add_filter( $tag, array( $a, 'filter' ), 12 );
 		$this->assertTrue( has_filter( $tag ) );
@@ -221,7 +221,7 @@ class Tests_Filters extends WP_UnitTestCase {
 	function test_filter_ref_array() {
 		$obj = new stdClass();
 		$a = new MockAction();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 
 		add_action($tag, array($a, 'filter'));
 
@@ -241,7 +241,7 @@ class Tests_Filters extends WP_UnitTestCase {
 		$obj = new stdClass();
 		$a = new MockAction();
 		$b = new MockAction();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 
 		add_action($tag, array($a, 'filter_append'), 10, 2);
 		add_action($tag, array($b, 'filter_append'), 10, 2);
@@ -274,8 +274,8 @@ class Tests_Filters extends WP_UnitTestCase {
 	 */
 	function test_has_filter_after_remove_all_filters() {
 		$a = new MockAction();
-		$tag = rand_str();
-		$val = rand_str();
+		$tag = __FUNCTION__;
+		$val = __FUNCTION__ . '_val';
 
 		// No priority
 		add_filter( $tag, array( $a, 'filter' ), 11 );
diff --git a/tests/phpunit/tests/general/document-title.php b/tests/phpunit/tests/general/document-title.php
index 0e5d282a40..7ba319666a 100644
--- a/tests/phpunit/tests/general/document-title.php
+++ b/tests/phpunit/tests/general/document-title.php
@@ -28,7 +28,6 @@ class Tests_General_DocumentTitle extends WP_UnitTestCase {
 		$this->post_id = $this->factory->post->create( array(
 			'post_author'  => $this->author_id,
 			'post_status'  => 'publish',
-			'post_content' => rand_str(),
 			'post_title'   => 'test_title',
 			'post_type'    => 'post',
 			'post_date'    => '2015-09-22 18:52:17',
diff --git a/tests/phpunit/tests/hooks/add_filter.php b/tests/phpunit/tests/hooks/add_filter.php
index 35ac55e7bc..79aeb755d6 100755
--- a/tests/phpunit/tests/hooks/add_filter.php
+++ b/tests/phpunit/tests/hooks/add_filter.php
@@ -13,7 +13,7 @@ class Tests_WP_Hook_Add_Filter extends WP_UnitTestCase {
 	public function test_add_filter_with_function() {
 		$callback = '__return_null';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -28,7 +28,7 @@ class Tests_WP_Hook_Add_Filter extends WP_UnitTestCase {
 		$a = new MockAction();
 		$callback = array( $a, 'action' );
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -42,7 +42,7 @@ class Tests_WP_Hook_Add_Filter extends WP_UnitTestCase {
 	public function test_add_filter_with_static_method() {
 		$callback = array( 'MockAction', 'action' );
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -57,7 +57,7 @@ class Tests_WP_Hook_Add_Filter extends WP_UnitTestCase {
 		$callback_one = '__return_null';
 		$callback_two = '__return_false';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -72,7 +72,7 @@ class Tests_WP_Hook_Add_Filter extends WP_UnitTestCase {
 		$callback_one = '__return_null';
 		$callback_two = '__return_false';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -87,7 +87,7 @@ class Tests_WP_Hook_Add_Filter extends WP_UnitTestCase {
 	public function test_readd_filter() {
 		$callback = '__return_null';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -101,7 +101,7 @@ class Tests_WP_Hook_Add_Filter extends WP_UnitTestCase {
 	public function test_readd_filter_with_different_priority() {
 		$callback = '__return_null';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -118,7 +118,7 @@ class Tests_WP_Hook_Add_Filter extends WP_UnitTestCase {
 		$b = new MockAction();
 		$c = new MockAction();
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 
 		$hook->add_filter( $tag, array( $a, 'action' ), 10, 1 );
 		$hook->add_filter( $tag, array( $b, 'action' ), 5, 1 );
diff --git a/tests/phpunit/tests/hooks/apply_filters.php b/tests/phpunit/tests/hooks/apply_filters.php
index 048a00a78f..06161b9bc7 100755
--- a/tests/phpunit/tests/hooks/apply_filters.php
+++ b/tests/phpunit/tests/hooks/apply_filters.php
@@ -11,10 +11,10 @@ class Tests_WP_Hook_Apply_Filters extends WP_UnitTestCase {
 		$a = new MockAction();
 		$callback = array( $a, 'filter' );
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
-		$arg = rand_str();
+		$arg = __FUNCTION__ . '_arg';
 
 		$hook->add_filter( $tag, $callback, $priority, $accepted_args );
 
@@ -28,10 +28,10 @@ class Tests_WP_Hook_Apply_Filters extends WP_UnitTestCase {
 		$a = new MockAction();
 		$callback = array( $a, 'filter' );
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
-		$arg = rand_str();
+		$arg = __FUNCTION__ . '_arg';
 
 		$hook->add_filter( $tag, $callback, $priority, $accepted_args );
 
diff --git a/tests/phpunit/tests/hooks/do_action.php b/tests/phpunit/tests/hooks/do_action.php
index b810d4690b..18d62521ac 100755
--- a/tests/phpunit/tests/hooks/do_action.php
+++ b/tests/phpunit/tests/hooks/do_action.php
@@ -19,10 +19,10 @@ class Tests_WP_Hook_Do_Action extends WP_UnitTestCase {
 		$a = new MockAction();
 		$callback = array( $a, 'action' );
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
-		$arg = rand_str();
+		$arg = __FUNCTION__ . '_arg';
 
 		$hook->add_filter( $tag, $callback, $priority, $accepted_args );
 		$hook->do_action( array( $arg ) );
@@ -34,10 +34,10 @@ class Tests_WP_Hook_Do_Action extends WP_UnitTestCase {
 		$a = new MockAction();
 		$callback = array( $a, 'filter' );
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
-		$arg = rand_str();
+		$arg = __FUNCTION__ . '_arg';
 
 		$hook->add_filter( $tag, $callback, $priority, $accepted_args );
 		$hook->do_action( array( $arg ) );
@@ -52,10 +52,10 @@ class Tests_WP_Hook_Do_Action extends WP_UnitTestCase {
 		$callback_one = array( $a, 'filter' );
 		$callback_two = array( $b, 'filter' );
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
-		$arg = rand_str();
+		$arg = __FUNCTION__ . '_arg';
 
 		$hook->add_filter( $tag, $callback_one, $priority, $accepted_args );
 		$hook->add_filter( $tag, $callback_two, $priority, $accepted_args );
@@ -71,10 +71,10 @@ class Tests_WP_Hook_Do_Action extends WP_UnitTestCase {
 		$callback_one = array( $a, 'filter' );
 		$callback_two = array( $b, 'filter' );
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
-		$arg = rand_str();
+		$arg = __FUNCTION__ . '_arg';
 
 		$hook->add_filter( $tag, $callback_one, $priority, $accepted_args );
 		$hook->add_filter( $tag, $callback_two, $priority, $accepted_args );
@@ -87,10 +87,10 @@ class Tests_WP_Hook_Do_Action extends WP_UnitTestCase {
 	public function test_do_action_with_no_accepted_args() {
 		$callback = array( $this, '_action_callback' );
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = 0;
-		$arg = rand_str();
+		$arg = __FUNCTION__ . '_arg';
 
 		$hook->add_filter( $tag, $callback, $priority, $accepted_args );
 		$hook->do_action( array( $arg ) );
@@ -101,10 +101,10 @@ class Tests_WP_Hook_Do_Action extends WP_UnitTestCase {
 	public function test_do_action_with_one_accepted_arg() {
 		$callback = array( $this, '_action_callback' );
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = 1;
-		$arg = rand_str();
+		$arg = __FUNCTION__ . '_arg';
 
 		$hook->add_filter( $tag, $callback, $priority, $accepted_args );
 		$hook->do_action( array( $arg ) );
@@ -115,10 +115,10 @@ class Tests_WP_Hook_Do_Action extends WP_UnitTestCase {
 	public function test_do_action_with_more_accepted_args() {
 		$callback = array( $this, '_action_callback' );
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = 1000;
-		$arg = rand_str();
+		$arg = __FUNCTION__ . '_arg';
 
 		$hook->add_filter( $tag, $callback, $priority, $accepted_args );
 		$hook->do_action( array( $arg ) );
diff --git a/tests/phpunit/tests/hooks/do_all_hook.php b/tests/phpunit/tests/hooks/do_all_hook.php
index a1e3586e84..6c6a0a9844 100755
--- a/tests/phpunit/tests/hooks/do_all_hook.php
+++ b/tests/phpunit/tests/hooks/do_all_hook.php
@@ -14,7 +14,7 @@ class Tests_WP_Hook_Do_All_Hook extends WP_UnitTestCase {
 		$tag = 'all';
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
-		$arg = rand_str();
+		$arg = 'all_arg';
 
 		$hook->add_filter( $tag, $callback, $priority, $accepted_args );
 		$args = array( $arg );
diff --git a/tests/phpunit/tests/hooks/has_filter.php b/tests/phpunit/tests/hooks/has_filter.php
index 0e65b4244c..86d965dc46 100755
--- a/tests/phpunit/tests/hooks/has_filter.php
+++ b/tests/phpunit/tests/hooks/has_filter.php
@@ -10,7 +10,7 @@ class Tests_WP_Hook_Has_Filter extends WP_UnitTestCase {
 	public function test_has_filter_with_function() {
 		$callback = '__return_null';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -23,7 +23,7 @@ class Tests_WP_Hook_Has_Filter extends WP_UnitTestCase {
 		$a = new MockAction();
 		$callback = array( $a, 'action' );
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -35,7 +35,7 @@ class Tests_WP_Hook_Has_Filter extends WP_UnitTestCase {
 	public function test_has_filter_with_static_method() {
 		$callback = array( 'MockAction', 'action' );
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -47,7 +47,7 @@ class Tests_WP_Hook_Has_Filter extends WP_UnitTestCase {
 	public function test_has_filter_without_callback() {
 		$callback = '__return_null';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -64,7 +64,7 @@ class Tests_WP_Hook_Has_Filter extends WP_UnitTestCase {
 	public function test_not_has_filter_with_callback() {
 		$callback = '__return_null';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 
 		$this->assertFalse( $hook->has_filter( $tag, $callback ) );
 	}
@@ -72,7 +72,7 @@ class Tests_WP_Hook_Has_Filter extends WP_UnitTestCase {
 	public function test_has_filter_with_wrong_callback() {
 		$callback = '__return_null';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
diff --git a/tests/phpunit/tests/hooks/has_filters.php b/tests/phpunit/tests/hooks/has_filters.php
index becf4413b3..3bc5f9f493 100755
--- a/tests/phpunit/tests/hooks/has_filters.php
+++ b/tests/phpunit/tests/hooks/has_filters.php
@@ -10,7 +10,7 @@ class Tests_WP_Hook_Has_Filters extends WP_UnitTestCase {
 	public function test_has_filters_with_callback() {
 		$callback = '__return_null';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -27,7 +27,7 @@ class Tests_WP_Hook_Has_Filters extends WP_UnitTestCase {
 	public function test_not_has_filters_with_removed_callback() {
 		$callback = '__return_null';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -39,7 +39,7 @@ class Tests_WP_Hook_Has_Filters extends WP_UnitTestCase {
 	public function test_not_has_filter_with_directly_removed_callback() {
 		$callback = '__return_null';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
diff --git a/tests/phpunit/tests/hooks/iterator.php b/tests/phpunit/tests/hooks/iterator.php
index 344d31d8f3..30b5580954 100755
--- a/tests/phpunit/tests/hooks/iterator.php
+++ b/tests/phpunit/tests/hooks/iterator.php
@@ -11,7 +11,7 @@ class Tests_WP_Hook_Iterator extends WP_UnitTestCase {
 		$callback_one = '__return_null';
 		$callback_two = '__return_false';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
diff --git a/tests/phpunit/tests/hooks/preinit_hooks.php b/tests/phpunit/tests/hooks/preinit_hooks.php
index e1d991c023..e00474b3c3 100755
--- a/tests/phpunit/tests/hooks/preinit_hooks.php
+++ b/tests/phpunit/tests/hooks/preinit_hooks.php
@@ -8,9 +8,9 @@
 class Tests_WP_Hook_Preinit_Hooks extends WP_UnitTestCase {
 
 	public function test_array_to_hooks() {
-		$tag1 = rand_str();
+		$tag1 = __FUNCTION__ . '_1';
 		$priority1 = rand( 1, 100 );
-		$tag2 = rand_str();
+		$tag2 = __FUNCTION__ . '_2';
 		$priority2 = rand( 1, 100 );
 		$filters = array(
 			$tag1 => array(
diff --git a/tests/phpunit/tests/hooks/remove_all_filters.php b/tests/phpunit/tests/hooks/remove_all_filters.php
index 57f4d83875..faf1858495 100755
--- a/tests/phpunit/tests/hooks/remove_all_filters.php
+++ b/tests/phpunit/tests/hooks/remove_all_filters.php
@@ -10,7 +10,7 @@ class Tests_WP_Hook_Remove_All_Filters extends WP_UnitTestCase {
 	public function test_remove_all_filters() {
 		$callback = '__return_null';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -25,7 +25,7 @@ class Tests_WP_Hook_Remove_All_Filters extends WP_UnitTestCase {
 		$callback_one = '__return_null';
 		$callback_two = '__return_false';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
diff --git a/tests/phpunit/tests/hooks/remove_filter.php b/tests/phpunit/tests/hooks/remove_filter.php
index 42a3f84623..b35b10f938 100755
--- a/tests/phpunit/tests/hooks/remove_filter.php
+++ b/tests/phpunit/tests/hooks/remove_filter.php
@@ -10,7 +10,7 @@ class Tests_WP_Hook_Remove_Filter extends WP_UnitTestCase {
 	public function test_remove_filter_with_function() {
 		$callback = '__return_null';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -24,7 +24,7 @@ class Tests_WP_Hook_Remove_Filter extends WP_UnitTestCase {
 		$a = new MockAction();
 		$callback = array( $a, 'action' );
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -37,7 +37,7 @@ class Tests_WP_Hook_Remove_Filter extends WP_UnitTestCase {
 	public function test_remove_filter_with_static_method() {
 		$callback = array( 'MockAction', 'action' );
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -51,7 +51,7 @@ class Tests_WP_Hook_Remove_Filter extends WP_UnitTestCase {
 		$callback_one = '__return_null';
 		$callback_two = '__return_false';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
@@ -67,7 +67,7 @@ class Tests_WP_Hook_Remove_Filter extends WP_UnitTestCase {
 		$callback_one = '__return_null';
 		$callback_two = '__return_false';
 		$hook = new WP_Hook();
-		$tag = rand_str();
+		$tag = __FUNCTION__;
 		$priority = rand( 1, 100 );
 		$accepted_args = rand( 1, 100 );
 
diff --git a/tests/phpunit/tests/image/functions.php b/tests/phpunit/tests/image/functions.php
index 9cc3f09d2a..6335df02af 100644
--- a/tests/phpunit/tests/image/functions.php
+++ b/tests/phpunit/tests/image/functions.php
@@ -306,7 +306,7 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 
 		$file = wp_crop_image( 'https://asdftestblog1.files.wordpress.com/2008/04/canola.jpg',
 							  0, 0, 100, 100, 100, 100, false,
-							  DIR_TESTDATA . '/images/' . rand_str() . '.jpg' );
+							  DIR_TESTDATA . '/images/' . __FUNCTION__ . '.jpg' );
 		$this->assertNotInstanceOf( 'WP_Error', $file );
 		$this->assertFileExists( $file );
 		$image = wp_get_image_editor( $file );
diff --git a/tests/phpunit/tests/link/getPreviewPostLink.php b/tests/phpunit/tests/link/getPreviewPostLink.php
index 40d1ee9614..c716844ca0 100644
--- a/tests/phpunit/tests/link/getPreviewPostLink.php
+++ b/tests/phpunit/tests/link/getPreviewPostLink.php
@@ -52,7 +52,7 @@ class Tests_Link_GetPreviewPostLink extends WP_UnitTestCase {
 	}
 
 	public function test_get_preview_post_link_should_return_empty_string_for_non_viewable_post_type() {
-		$post_type = register_post_type( rand_str(12), array(
+		$post_type = register_post_type( 'non_viewable_cpt', array(
 			'public' => false,
 		) );
 
diff --git a/tests/phpunit/tests/meta.php b/tests/phpunit/tests/meta.php
index eb6f2c51af..bdd5529cc3 100644
--- a/tests/phpunit/tests/meta.php
+++ b/tests/phpunit/tests/meta.php
@@ -161,7 +161,7 @@ class Tests_Meta extends WP_UnitTestCase {
 	}
 
 	function test_metadata_slashes() {
-		$key = rand_str();
+		$key = __FUNCTION__;
 		$value = 'Test\\singleslash';
 		$expected = 'Testsingleslash';
 		$value2 = 'Test\\\\doubleslash';
diff --git a/tests/phpunit/tests/multisite/getSpaceUsed.php b/tests/phpunit/tests/multisite/getSpaceUsed.php
index cbc5138453..be1364a8f0 100644
--- a/tests/phpunit/tests/multisite/getSpaceUsed.php
+++ b/tests/phpunit/tests/multisite/getSpaceUsed.php
@@ -35,8 +35,8 @@ class Tests_Multisite_Get_Space_Used extends WP_UnitTestCase {
 		}
 
 		// Upload a file to the new site.
-		$filename = rand_str().'.jpg';
-		$contents = rand_str();
+		$filename = __FUNCTION__ . '.jpg';
+		$contents = __FUNCTION__ . '_contents';
 		$file = wp_upload_bits( $filename, null, $contents );
 
 		// get_space_used() is measures in MB, get the size of the new file in MB.
@@ -71,8 +71,8 @@ class Tests_Multisite_Get_Space_Used extends WP_UnitTestCase {
 		}
 
 		// Upload a file to the new site.
-		$filename = rand_str().'.jpg';
-		$contents = rand_str();
+		$filename = __FUNCTION__ . '.jpg';
+		$contents = __FUNCTION__ . '_contents';
 		wp_upload_bits( $filename, null, $contents );
 
 		restore_current_blog();
diff --git a/tests/phpunit/tests/multisite/ms-files-rewriting.php b/tests/phpunit/tests/multisite/ms-files-rewriting.php
index 8bc87df7d2..38be416aac 100644
--- a/tests/phpunit/tests/multisite/ms-files-rewriting.php
+++ b/tests/phpunit/tests/multisite/ms-files-rewriting.php
@@ -61,8 +61,8 @@ class Tests_Multisite_MS_Files_Rewriting extends WP_UnitTestCase {
 	 * should change with upload directories.
 	 */
 	function test_upload_directories_after_multiple_wpmu_delete_blog_with_ms_files() {
-		$filename = rand_str().'.jpg';
-		$contents = rand_str();
+		$filename = __FUNCTION__ . '.jpg';
+		$contents = __FUNCTION__ . '_contents';
 
 		// Upload a file to the main site on the network.
 		$file1 = wp_upload_bits( $filename, null, $contents );
diff --git a/tests/phpunit/tests/multisite/site.php b/tests/phpunit/tests/multisite/site.php
index ddf01163f7..37f52941c9 100644
--- a/tests/phpunit/tests/multisite/site.php
+++ b/tests/phpunit/tests/multisite/site.php
@@ -270,8 +270,8 @@ class Tests_Multisite_Site extends WP_UnitTestCase {
 	 * should change with upload directories.
 	 */
 	function test_upload_directories_after_multiple_wpmu_delete_blog() {
-		$filename = rand_str().'.jpg';
-		$contents = rand_str();
+		$filename = __FUNCTION__ . '.jpg';
+		$contents = __FUNCTION__ . '_contents';
 
 		// Upload a file to the main site on the network.
 		$file1 = wp_upload_bits( $filename, null, $contents );
diff --git a/tests/phpunit/tests/oembed/WpEmbed.php b/tests/phpunit/tests/oembed/WpEmbed.php
index 8fe8ae661b..9a46e1f3af 100644
--- a/tests/phpunit/tests/oembed/WpEmbed.php
+++ b/tests/phpunit/tests/oembed/WpEmbed.php
@@ -64,7 +64,7 @@ class Tests_WP_Embed extends WP_UnitTestCase {
 	}
 
 	public function test_wp_embed_register_handler() {
-		$handle   = rand_str();
+		$handle   = __FUNCTION__;
 		$regex    = '#https?://example\.com/embed/([^/]+)#i';
 		$callback = array( $this, '_embed_handler_callback' );
 
@@ -102,7 +102,7 @@ class Tests_WP_Embed extends WP_UnitTestCase {
 	}
 
 	public function test_autoembed_should_return_modified_content() {
-		$handle   = rand_str();
+		$handle   = __FUNCTION__;
 		$regex    = '#https?://example\.com/embed/([^/]+)#i';
 		$callback = array( $this, '_embed_handler_callback' );
 
diff --git a/tests/phpunit/tests/option/multisite.php b/tests/phpunit/tests/option/multisite.php
index 5cde7ba126..0669a7adc6 100644
--- a/tests/phpunit/tests/option/multisite.php
+++ b/tests/phpunit/tests/option/multisite.php
@@ -25,10 +25,10 @@ class Tests_Multisite_Option extends WP_UnitTestCase {
 	}
 
 	function test_from_same_site() {
-		$key = rand_str();
-		$key2 = rand_str();
-		$value = rand_str();
-		$value2 = rand_str();
+		$key    = __FUNCTION__ . '_1';
+		$key2   = __FUNCTION__ . '_2';
+		$value  = __FUNCTION__ . '_val1';
+		$value2 = __FUNCTION__ . '_val2';
 
 		$this->assertFalse( get_blog_option( 1, 'doesnotexist' ) );
 		$this->assertFalse( get_option( 'doesnotexist' ) ); // check get_option()
@@ -62,10 +62,10 @@ class Tests_Multisite_Option extends WP_UnitTestCase {
 	}
 
 	function test_from_same_site_with_null_blog_id() {
-		$key = rand_str();
-		$key2 = rand_str();
-		$value = rand_str();
-		$value2 = rand_str();
+		$key    = __FUNCTION__ . '_1';
+		$key2   = __FUNCTION__ . '_2';
+		$value  = __FUNCTION__ . '_val1';
+		$value2 = __FUNCTION__ . '_val2';
 
 		$this->assertFalse( get_blog_option( null, 'doesnotexist' ) );
 		$this->assertFalse( get_option( 'doesnotexist' ) ); // check get_option()
@@ -109,10 +109,10 @@ class Tests_Multisite_Option extends WP_UnitTestCase {
 		) );
 		$this->assertInternalType( 'integer', $blog_id );
 
-		$key = rand_str();
-		$key2 = rand_str();
-		$value = rand_str();
-		$value2 = rand_str();
+		$key    = __FUNCTION__ . '_key1';
+		$key2   = __FUNCTION__ . '_key2';
+		$value  = __FUNCTION__ . '_val1';
+		$value2 = __FUNCTION__ . '_val2';
 
 		$this->assertFalse( get_blog_option( $blog_id, 'doesnotexist' ) );
 		//$this->assertFalse( get_option( 'doesnotexist' ) ); // check get_option()