[ticket/11615] Rename init_test to creation_test for clarity

PHPBB3-11615
[ticket/11615] Rename class in file to match

PHPBB3-11615
[ticket/11615] Remove magic number in creation_test

Removing this magic number to its own variable
with clean multiplication makes it clear
what the number represents.

PHPBB3-11615
[ticket/11615] Fix typo in creation_test

PHPBB3-11615