Unit tests for WP#18158

[bananastalktome]

First real unit tests here, so feedback is appreciated. Tests 'NOT EXISTS' compare for metadata. Unit tests for ​WP:#18158 .

Why is this line necessary:

delete_metadata( 'user', $this->author->ID, 'meta_key' );

Should the users be created explicitly with?

$this->factory->user->create();

@scribu This may be an unnecessary check, but I was ensuring that, once the metadata was removed, the same type of assertion from line ~92 (with the 'NOT EXISTS' compare for 'meta_key') would then return that user. Would this be best to leave out of this particular test / is it covered already by other tests?

@kurtpayne Besides the default admin user, a user for this test is already created in the setUp method of Tests_Meta, correct?

Again, I'm new to unit testing and feedback like this is very helpful for me. Thanks!

(In [973]) add test_user_metadata_not_exists(). props bananastalktome. fixes #115

(In [974]) clearer formatting of queries in test_user_metadata_not_exists(). see #115