diff --git a/tests/phpunit/includes/testcase-rest-post-type-controller.php b/tests/phpunit/includes/testcase-rest-post-type-controller.php
index 0a13d81586..49c2ebaf9c 100644
--- a/tests/phpunit/includes/testcase-rest-post-type-controller.php
+++ b/tests/phpunit/includes/testcase-rest-post-type-controller.php
@@ -271,9 +271,9 @@ abstract class WP_Test_REST_Post_Type_Controller_Testcase extends WP_Test_REST_C
 
 	protected function set_post_data( $args = array() ) {
 		$defaults = array(
-			'title'   => rand_str(),
-			'content' => rand_str(),
-			'excerpt' => rand_str(),
+			'title'   => 'Post Title',
+			'content' => 'Post content',
+			'excerpt' => 'Post excerpt',
 			'name'    => 'test',
 			'status'  => 'publish',
 			'author'  => get_current_user_id(),
@@ -286,13 +286,13 @@ abstract class WP_Test_REST_Post_Type_Controller_Testcase extends WP_Test_REST_C
 	protected function set_raw_post_data( $args = array() ) {
 		return wp_parse_args( $args, $this->set_post_data( array(
 			'title'   => array(
-				'raw' => rand_str(),
+				'raw' => 'Post Title',
 			),
 			'content' => array(
-				'raw' => rand_str(),
+				'raw' => 'Post content',
 			),
 			'excerpt' => array(
-				'raw' => rand_str(),
+				'raw' => 'Post excerpt',
 			),
 		) ) );
 	}
diff --git a/tests/phpunit/tests/option/networkOption.php b/tests/phpunit/tests/option/networkOption.php
index 612949f208..17e96bd8fc 100644
--- a/tests/phpunit/tests/option/networkOption.php
+++ b/tests/phpunit/tests/option/networkOption.php
@@ -17,8 +17,8 @@ class Tests_Option_NetworkOption extends WP_UnitTestCase {
 		}
 
 		$id = self::factory()->network->create();
-		$option = rand_str();
-		$value = rand_str();
+		$option = __FUNCTION__;
+		$value = __FUNCTION__;
 
 		add_site_option( $option, $value );
 		$this->assertFalse( get_network_option( $id, $option, false ) );
@@ -30,8 +30,8 @@ class Tests_Option_NetworkOption extends WP_UnitTestCase {
 		}
 
 		$id = self::factory()->network->create();
-		$option = rand_str();
-		$value = rand_str();
+		$option = __FUNCTION__;
+		$value = __FUNCTION__;
 
 		add_network_option( $id, $option, $value );
 		$this->assertEquals( $value, get_network_option( $id, $option, false ) );
@@ -43,8 +43,8 @@ class Tests_Option_NetworkOption extends WP_UnitTestCase {
 		}
 
 		$id = self::factory()->network->create();
-		$option = rand_str();
-		$value = rand_str();
+		$option = __FUNCTION__;
+		$value = __FUNCTION__;
 
 		add_site_option( $option, $value );
 		add_network_option( $id, $option, $value );
@@ -56,7 +56,7 @@ class Tests_Option_NetworkOption extends WP_UnitTestCase {
 	 * @ticket 22846
 	 */
 	public function test_add_network_option_is_not_stored_as_autoload_option() {
-		$key = rand_str();
+		$key = __FUNCTION__;
 
 		if ( is_multisite() ) {
 			$this->markTestSkipped( 'Does not apply when used in multisite.' );
@@ -73,7 +73,7 @@ class Tests_Option_NetworkOption extends WP_UnitTestCase {
 	 * @ticket 22846
 	 */
 	public function test_update_network_option_is_not_stored_as_autoload_option() {
-		$key = rand_str();
+		$key = __FUNCTION__;
 
 		if ( is_multisite() ) {
 			$this->markTestSkipped( 'Does not apply when used in multisite.' );
diff --git a/tests/phpunit/tests/option/option.php b/tests/phpunit/tests/option/option.php
index fea674dd53..f020bee861 100644
--- a/tests/phpunit/tests/option/option.php
+++ b/tests/phpunit/tests/option/option.php
@@ -72,7 +72,7 @@ class Tests_Option_Option extends WP_UnitTestCase {
 	}
 
 	function test_serialized_data() {
-		$key = rand_str();
+		$key = __FUNCTION__;
 		$value = array( 'foo' => true, 'bar' => true );
 
 		$this->assertTrue( add_option( $key, $value ) );
diff --git a/tests/phpunit/tests/option/siteOption.php b/tests/phpunit/tests/option/siteOption.php
index b5f178c734..eff9391c57 100644
--- a/tests/phpunit/tests/option/siteOption.php
+++ b/tests/phpunit/tests/option/siteOption.php
@@ -13,24 +13,24 @@ class Tests_Option_SiteOption extends WP_UnitTestCase {
 	}
 
 	function test_get_site_option_returns_false_after_deletion() {
-		$key = rand_str();
-		$value = rand_str();
+		$key = __FUNCTION__;
+		$value = __FUNCTION__;
 		add_site_option( $key, $value );
 		delete_site_option( $key );
 		$this->assertFalse( get_site_option( $key ) );
 	}
 
 	function test_get_site_option_returns_value() {
-		$key = rand_str();
-		$value = rand_str();
+		$key = __FUNCTION__;
+		$value = __FUNCTION__;
 		add_site_option( $key, $value );
 		$this->assertEquals( $value, get_site_option( $key ) );
 	}
 
 	function test_get_site_option_returns_updated_value() {
-		$key = rand_str();
-		$value = rand_str();
-		$new_value = rand_str();
+		$key = __FUNCTION__;
+		$value = __FUNCTION__ . '_1';
+		$new_value = __FUNCTION__ . '_2';
 		add_site_option( $key, $value );
 		update_site_option( $key, $new_value );
 		$this->assertEquals( $new_value, get_site_option( $key ) );
@@ -55,15 +55,15 @@ class Tests_Option_SiteOption extends WP_UnitTestCase {
 	}
 
 	function test_get_site_option_exists_does_not_return_provided_default() {
-		$key = rand_str();
-		$value = rand_str();
+		$key = __FUNCTION__;
+		$value = __FUNCTION__;
 		add_site_option( $key, $value );
 		$this->assertEquals( $value, get_site_option( $key, 'foo' ) );
 	}
 
 	function test_get_site_option_exists_does_not_return_filtered_default() {
-		$key = rand_str();
-		$value = rand_str();
+		$key = __FUNCTION__;
+		$value = __FUNCTION__;
 		add_site_option( $key, $value );
 		add_filter( 'default_site_option_' . $key , array( $this, '__return_foo' ) );
 		$site_option = get_site_option( $key );
@@ -72,21 +72,21 @@ class Tests_Option_SiteOption extends WP_UnitTestCase {
 	}
 
 	function test_add_site_option_returns_true_for_new_option() {
-		$key = rand_str();
-		$value = rand_str();
+		$key = __FUNCTION__;
+		$value = __FUNCTION__;
 		$this->assertTrue( add_site_option( $key, $value ) );
 	}
 
 	function test_add_site_option_returns_false_for_existing_option() {
-		$key = rand_str();
-		$value = rand_str();
+		$key = __FUNCTION__;
+		$value = __FUNCTION__;
 		add_site_option( $key, $value );
 		$this->assertFalse( add_site_option( $key, $value ) );
 	}
 
 	function test_update_site_option_returns_false_for_same_value() {
-		$key = rand_str();
-		$value = rand_str();
+		$key = __FUNCTION__;
+		$value = __FUNCTION__;
 		add_site_option( $key, $value );
 		$this->assertFalse( update_site_option( $key, $value ) );
 	}
@@ -100,29 +100,29 @@ class Tests_Option_SiteOption extends WP_UnitTestCase {
 	}
 
 	function test_delete_site_option_returns_true_if_option_exists() {
-		$key = rand_str();
-		$value = rand_str();
+		$key = __FUNCTION__;
+		$value = __FUNCTION__;
 		add_site_option( $key, $value );
 		$this->assertTrue( delete_site_option( $key ) );
 	}
 
 	function test_delete_site_option_returns_false_if_option_does_not_exist() {
-		$key = rand_str();
-		$value = rand_str();
+		$key = __FUNCTION__;
+		$value = __FUNCTION__;
 		add_site_option( $key, $value );
 		delete_site_option( $key );
 		$this->assertFalse( delete_site_option( $key ) );
 	}
 
 	function test_site_option_add_and_get_serialized_array() {
-		$key = rand_str();
+		$key = __FUNCTION__;
 		$value = array( 'foo' => true, 'bar' => true );
 		add_site_option( $key, $value );
 		$this->assertEquals( $value, get_site_option( $key ) );
 	}
 
 	function test_site_option_add_and_get_serialized_object() {
-		$key = rand_str();
+		$key = __FUNCTION__;
 		$value = new stdClass();
 		$value->foo = true;
 		$value->bar = true;
@@ -132,7 +132,7 @@ class Tests_Option_SiteOption extends WP_UnitTestCase {
 
 	// #15497 - ensure update_site_option will add options with false-y values
 	function test_update_adds_falsey_value() {
-		$key = rand_str();
+		$key = __FUNCTION__;
 		$value = 0;
 
 		delete_site_option( $key );
@@ -143,7 +143,7 @@ class Tests_Option_SiteOption extends WP_UnitTestCase {
 
 	// #18955 - ensure get_site_option doesn't cache the default value for non-existent options
 	function test_get_doesnt_cache_default_value() {
-		$option = rand_str();
+		$option = __FUNCTION__;
 		$default = 'a default';
 
 		$this->assertEquals( get_site_option( $option, $default ), $default );
diff --git a/tests/phpunit/tests/option/siteTransient.php b/tests/phpunit/tests/option/siteTransient.php
index 29aab46ac6..4a9f0e2d38 100644
--- a/tests/phpunit/tests/option/siteTransient.php
+++ b/tests/phpunit/tests/option/siteTransient.php
@@ -30,7 +30,7 @@ class Tests_Option_SiteTransient extends WP_UnitTestCase {
 	}
 
 	function test_serialized_data() {
-		$key = rand_str();
+		$key = __FUNCTION__;
 		$value = array( 'foo' => true, 'bar' => true );
 
 		$this->assertTrue( set_site_transient( $key, $value ) );
@@ -46,7 +46,7 @@ class Tests_Option_SiteTransient extends WP_UnitTestCase {
 	 * @ticket 22846
 	 */
 	public function test_set_site_transient_is_not_stored_as_autoload_option() {
-		$key = rand_str();
+		$key = 'not_autoloaded';
 
 		if ( is_multisite() ) {
 			$this->markTestSkipped( 'Does not apply when used in multisite.' );