Refactoring tests

[carusogabriel]

I've refactored several tests, using:

• assertCount instead of count function;
• assertInternalType instead of is_* functions;
• assertArrayHasKey and assertArrayNotHasKey instead of array_key_exists function;
• assertTrue instead of comparison with true keyword;
• assertFalse instead of comparison with false keyword;
• assertNull instead of comparison with null keyword;
• assertContains and assertNotContains instead of in_array function;
• assertObjectNotHasAttribute instead of isset function;
• assertLessThan for mathematical comparisons.

[jenssegers]

Thanks!