Replace assertions involving calls to empty() with assertEmpty()/assertNotEmpty()/assertArrayNotHasKey()

Problem/Motivation

As title.

Proposed resolution

For example:

-    $this->assertFalse(!empty($view->build_info['pre_render_called']), 'Make sure hook_views_pre_render is not called for the cached view.');
+    $this->assertEmpty($view->build_info['pre_render_called']);

Not sure about whether to keep or drop the $message arguments here, though.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet