Test the progress display

'progress.c' has seen a few fixes recently [1], and, unfortunately,
some of those fixes required further fixes [2].  It seems it's time to
have a few tests focusing on the subtleties of the progress display.

Add the 'test-tool progress' subcommand to help testing the progress
display, reading instructions from standard input and turning them
into calls to the display_progress() and display_throughput()
functions with the given parameters.

The progress display is, however, critically dependent on timing,
because it's only updated once every second or, if the toal is known
in advance, every 1%, and there is the throughput rate as well.  These
make the progress display far too undeterministic for testing as-is.
To address this, add a few testing-specific variables and functions to
'progress.c', allowing the the new test helper to:

  - Disable the triggered-every-second SIGALRM and set the
    'progress_update' flag explicitly based in the input instructions.
    This way the progress line will be updated deterministically when
    the test wants it to be updated.

  - Specify the time elapsed since start_progress() to make the
    throughput rate calculations deterministic.

Add the new test script 't0500-progress-display.sh' to check a few
simple cases with and without throughput, and that a shorter progress
line properly covers up the previously displayed line in different
situations.

[1] See commits 545dc345eb (progress: break too long progress bar
    lines, 2019-04-12) and 9f1fd84e15 (progress: clear previous
    progress update dynamically, 2019-04-12).
[2] 1aed1a5f25 (progress: avoid empty line when breaking the progress
    line, 2019-05-19)

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 30 insertions, 2 deletions

diff --git a/progress.c b/progress.c
index 0eddf1804d..0063559aab 100644
--- a/progress.c
+++ b/progress.c
@@ -45,6 +45,19 @@ struct progress {
 
 static volatile sig_atomic_t progress_update;
 
+/*
+ * These are only intended for testing the progress output, i.e. exclusively
+ * for 'test-tool progress'.
+ */
+int progress_testing;
+uint64_t progress_test_ns = 0;
+void progress_test_force_update(void); /* To silence -Wmissing-prototypes */
+void progress_test_force_update(void)
+{
+	progress_update = 1;
+}
+
+
 static void progress_interval(int signum)
 {
 	progress_update = 1;
@@ -55,6 +68,9 @@ static void set_progress_signal(void)
 	struct sigaction sa;
 	struct itimerval v;
 
+	if (progress_testing)
+		return;
+
 	progress_update = 0;
 
 	memset(&sa, 0, sizeof(sa));
@@ -72,6 +88,10 @@ static void set_progress_signal(void)
 static void clear_progress_signal(void)
 {
 	struct itimerval v = {{0,},};
+
+	if (progress_testing)
+		return;
+
 	setitimer(ITIMER_REAL, &v, NULL);
 	signal(SIGALRM, SIG_IGN);
 	progress_update = 0;
@@ -154,6 +174,14 @@ static void throughput_string(struct strbuf *buf, uint64_t total,
 	strbuf_humanise_rate(buf, rate * 1024);
 }
 
+static uint64_t progress_getnanotime(struct progress *progress)
+{
+	if (progress_testing)
+		return progress->start_ns + progress_test_ns;
+	else
+		return getnanotime();
+}
+
 void display_throughput(struct progress *progress, uint64_t total)
 {
 	struct throughput *tp;
@@ -164,7 +192,7 @@ void display_throughput(struct progress *progress, uint64_t total)
 		return;
 	tp = progress->throughput;
 
-	now_ns = getnanotime();
+	now_ns = progress_getnanotime(progress);
 
 	if (!tp) {
 		progress->throughput = tp = xcalloc(1, sizeof(*tp));
@@ -296,7 +324,7 @@ void stop_progress_msg(struct progress **p_progress, const char *msg)
 		struct throughput *tp = progress->throughput;
 
 		if (tp) {
-			uint64_t now_ns = getnanotime();
+			uint64_t now_ns = progress_getnanotime(progress);
 			unsigned int misecs, rate;
 			misecs = ((now_ns - progress->start_ns) * 4398) >> 32;
 			rate = tp->curr_total / (misecs ? misecs : 1);