t7800: improve test descriptions with empty arguments

Some of the tests in t7800 are executed repeatedly in a loop with
different arguments. To distinguish these tests, the value of that
variable is rendered into the test title. But given that one of the
values is the empty string, it results in a somewhat awkward test name:

    difftool  ignores exit code

Improve this by printing "without options" in case the value is empty.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

t/t7800-difftool.sh

@@ -93,40 +93,40 @@ test_expect_success 'difftool forwards arguments to diff' '
 
 for opt in '' '--dir-diff'
 do
-	test_expect_success "difftool ${opt} ignores exit code" "
+	test_expect_success "difftool ${opt:-without options} ignores exit code" "
 		test_config difftool.error.cmd false &&
 		git difftool ${opt} -y -t error branch
 	"
 
-	test_expect_success "difftool ${opt} forwards exit code with --trust-exit-code" "
+	test_expect_success "difftool ${opt:-without options} forwards exit code with --trust-exit-code" "
 		test_config difftool.error.cmd false &&
 		test_must_fail git difftool ${opt} -y --trust-exit-code -t error branch
 	"
 
-	test_expect_success "difftool ${opt} forwards exit code with --trust-exit-code for built-ins" "
+	test_expect_success "difftool ${opt:-without options} forwards exit code with --trust-exit-code for built-ins" "
 		test_config difftool.vimdiff.path false &&
 		test_must_fail git difftool ${opt} -y --trust-exit-code -t vimdiff branch
 	"
 
-	test_expect_success "difftool ${opt} honors difftool.trustExitCode = true" "
+	test_expect_success "difftool ${opt:-without options} honors difftool.trustExitCode = true" "
 		test_config difftool.error.cmd false &&
 		test_config difftool.trustExitCode true &&
 		test_must_fail git difftool ${opt} -y -t error branch
 	"
 
-	test_expect_success "difftool ${opt} honors difftool.trustExitCode = false" "
+	test_expect_success "difftool ${opt:-without options} honors difftool.trustExitCode = false" "
 		test_config difftool.error.cmd false &&
 		test_config difftool.trustExitCode false &&
 		git difftool ${opt} -y -t error branch
 	"
 
-	test_expect_success "difftool ${opt} ignores exit code with --no-trust-exit-code" "
+	test_expect_success "difftool ${opt:-without options} ignores exit code with --no-trust-exit-code" "
 		test_config difftool.error.cmd false &&
 		test_config difftool.trustExitCode true &&
 		git difftool ${opt} -y --no-trust-exit-code -t error branch
 	"
 
-	test_expect_success "difftool ${opt} stops on error with --trust-exit-code" "
+	test_expect_success "difftool ${opt:-without options} stops on error with --trust-exit-code" "
 		test_when_finished 'rm -f for-diff .git/fail-right-file' &&
 		test_when_finished 'git reset -- for-diff' &&
 		write_script .git/fail-right-file <<-\EOF &&
@@ -140,7 +140,7 @@ do
 		test_line_count = 1 actual
 	"
 
-	test_expect_success "difftool ${opt} honors exit status if command not found" "
+	test_expect_success "difftool ${opt:-without options} honors exit status if command not found" "
 		test_config difftool.nonexistent.cmd i-dont-exist &&
 		test_config difftool.trustExitCode false &&
 		if test "${opt}" = '--dir-diff'