Make runAllTests() consistent with listTests().

This change has the listTests() function return
a string slice of all the tests. Originally, I
planned not to modify the listTests() function
and instead capture the output of it and then
iterate through the captured output. I decided
against this approach as most of the test binaries
already produce a slice as they collect tests
through filepath.Walk(). Now I use this slice
and return it so that I can iterate through in
runAllTests() and also when printing out the tests.

PiperOrigin-RevId: 259599782

0 files changed, 0 insertions, 0 deletions