diff --git a/tests/phpunit/tests/filesystem/base.php b/tests/phpunit/tests/filesystem/base.php
index f186cbb961..54fcb3e1e9 100644
--- a/tests/phpunit/tests/filesystem/base.php
+++ b/tests/phpunit/tests/filesystem/base.php
@@ -29,7 +29,7 @@ abstract class WP_Filesystem_UnitTestCase extends WP_UnitTestCase {
 
 	function test_is_MockFS_sane() {
 		global $wp_filesystem;
-		$this->assertTrue( is_a( $wp_filesystem, 'WP_Filesystem_MockFS' ) );
+		$this->assertInstanceOf( 'WP_Filesystem_MockFS', $wp_filesystem );
 
 		$wp_filesystem->init( '/' );
 
diff --git a/tests/phpunit/tests/post/query.php b/tests/phpunit/tests/post/query.php
index 686f77a293..6ccf69f534 100644
--- a/tests/phpunit/tests/post/query.php
+++ b/tests/phpunit/tests/post/query.php
@@ -102,7 +102,7 @@ class Tests_Post_Query extends WP_UnitTestCase {
 		foreach ( $query->posts as $post ) {
 
 			// Posts are WP_Post objects.
-			$this->assertTrue( is_a( $post, 'WP_Post' ) );
+			$this->assertInstanceOf( 'WP_Post', $post );
 
 			// Filters are raw.
 			$this->assertSame( 'raw', $post->filter );
diff --git a/tests/phpunit/tests/sitemaps/functions.php b/tests/phpunit/tests/sitemaps/functions.php
index aa4c63cc41..a4913fae5f 100644
--- a/tests/phpunit/tests/sitemaps/functions.php
+++ b/tests/phpunit/tests/sitemaps/functions.php
@@ -55,7 +55,7 @@ class Test_Sitemaps_Functions extends WP_UnitTestCase {
 		$this->assertSame( array_keys( $expected ), array_keys( $sitemaps ), 'Unable to confirm default sitemap types are registered.' );
 
 		foreach ( $expected as $name => $provider ) {
-			$this->assertTrue( is_a( $sitemaps[ $name ], $provider ), "Default $name sitemap is not a $provider object." );
+			$this->assertInstanceOf( $provider, $sitemaps[ $name ], "Default $name sitemap is not a $provider object." );
 		}
 	}
 
diff --git a/tests/phpunit/tests/taxonomy.php b/tests/phpunit/tests/taxonomy.php
index 8e256f8928..241cc26a98 100644
--- a/tests/phpunit/tests/taxonomy.php
+++ b/tests/phpunit/tests/taxonomy.php
@@ -438,7 +438,7 @@ class Tests_Taxonomy extends WP_UnitTestCase {
 			'taxonomy' => 'force_error',
 			'cat_name' => 'Error',
 		);
-		$this->assertTrue( is_a( wp_insert_category( $cat, true ), 'WP_Error' ) );
+		$this->assertInstanceOf( 'WP_Error', wp_insert_category( $cat, true ) );
 	}
 
 	function test_insert_category_force_error_no_handle() {