Build/Test Tools: Reduce the use of unnecessary randomness in tests.

This increases the overall reliability of the tests.

Props johnillo

Fixes #37371


git-svn-id: https://develop.svn.wordpress.org/trunk@52389 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/file.php

@@ -96,8 +96,8 @@ class Tests_File extends WP_UnitTestCase {
 			return false;
 		}
 
-		// Write some random contents.
-		$c = rand_str();
+		// Write some contents.
+		$c = 'foo';
 		fwrite( $fp, $c );
 		fclose( $fp );