Add some more methods to phpunit hhi

tests/definitions.hhi

@@ -2,10 +2,16 @@
 
 namespace {
   class PHPUnit_Framework_TestCase {
+    public function assertSame(mixed $expect, mixed $actual, ?string $msg = null);
+    public function assertNotSame(mixed $expect, mixed $actual, ?string $msg = null);
     public function assertEquals(mixed $expect, mixed $actual, ?string $msg = null);
     public function assertNotEquals(mixed $expect, mixed $actual, ?string $msg = null);
     public function assertContains(mixed $key, array $array, ?string $msg = null);
     public function assertNotContains(mixed $key, array $array, ?string $msg = null);
+    public function assertInstanceOf(string $expected, mixed $actual, ?string $msg = null);
+    public function assertNotInstanceOf(string $expected, mixed $actual, ?string $msg = null);
+    public function assertNull(mixed $actual, ?string $msg = null);
+    public function assertNotNull(mixed $actual, ?string $msg = null);
     public function fail(string $msg);
   }
 }