Files in tests directory should be ignored when they lack a .zunit extension

[NReilingh]

Currently, every file in the tests directory is treated as a zunit test file, and an error is thrown if the file does not start with the zunit shebang:

zunit/src/commands/run.zsh

Lines 396 to 425 in 8048638

	if [[ -d $argument ]]; then
	# Loop through each of the files in the directory
	for file in $(find $argument -mindepth 1 -maxdepth 1); do
	# Run it through the parser again
	_zunit_parse_argument $file
	done
	return
	fi
	# If it is a valid file
	if [[ -f $argument ]]; then
	# Grab the first line of the file
	line=$(cat $argument | head -n 1)
	# Check for the zunit shebang
	if [[ $line =~ "#! ?/usr/bin/env zunit" ]]; then
	# Add it to the array
	testfiles[(( ${#testfiles} + 1 ))]=("$argument${test_name+"@$test_name"}")
	return
	fi
	# The test file does not contain the zunit shebang, therefore
	# we can't trust that running it will not be harmful, and throw
	# a fatal error
	echo $(color red "File '$argument' is not a valid zunit test file") >&2
	echo "Test files must contain the following shebang on the first line" >&2
	echo " #!/usr/bin/env zunit" >&2
	exit 126
	fi

Is there a reason for not filtering out files that lack the .zunit extension? I have experienced a number of situations where zunit fails due to trying to read a macOS .DS_Store or vim .swp file as a test file.