CacheClearCase::testClearArray() sets a persistent variable that has no effect

CacheClearCase::testClearArray() contains the following code.

// Set the cache clear threshold to 2 to confirm that the full bin is cleared
// when the threshold is exceeded.
variable_set('cache_clear_threshold', 2);

That persistent variable is not used from Drupal code. With git grep --fixed-strings 'cache_clear_threshold', I get the following output.

modules/simpletest/tests/cache.test: variable_set('cache_clear_threshold', 2);

Those lines need to be removed.