Without this, execution continues beyond the end of the function, into the great unknown (probably eventually falling into either code left from a previous test, or the start of the DSP ROM). end_of_test is just an infinite loop to stop executing until the DSP is reset.
This makes the point where execution starts more obvious compared to a start_of_test label at the end of the include, and allows putting other functions at the start of the file. This change also modifies the existing tests to build with this change.
Pokechu22