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>

3 files changed, 83 insertions, 0 deletions

diff --git a/t/helper/test-progress.c b/t/helper/test-progress.c
new file mode 100644
index 0000000000..4e9f7fafdf
--- /dev/null
+++ b/t/helper/test-progress.c
@@ -0,0 +1,81 @@
+/*
+ * A test helper to exercise the progress display.
+ *
+ * Reads instructions from standard input, one instruction per line:
+ *
+ *   "progress <items>" - Call display_progress() with the given item count
+ *                        as parameter.
+ *   "throughput <bytes> <millis> - Call display_throughput() with the given
+ *                                  byte count as parameter.  The 'millis'
+ *                                  specify the time elapsed since the
+ *                                  start_progress() call.
+ *   "update" - Set the 'progress_update' flag.
+ *
+ * See 't0500-progress-display.sh' for examples.
+ */
+#include "test-tool.h"
+#include "gettext.h"
+#include "parse-options.h"
+#include "progress.h"
+#include "strbuf.h"
+
+/*
+ * These are defined in 'progress.c', but are not exposed in 'progress.h',
+ * because they are exclusively for testing.
+ */
+extern int progress_testing;
+extern uint64_t progress_test_ns;
+void progress_test_force_update(void);
+
+int cmd__progress(int argc, const char **argv)
+{
+	uint64_t total = 0;
+	const char *title;
+	struct strbuf line = STRBUF_INIT;
+	struct progress *progress;
+
+	const char *usage[] = {
+		"test-tool progress [--total=<n>] <progress-title>",
+		NULL
+	};
+	struct option options[] = {
+		OPT_INTEGER(0, "total", &total, "total number of items"),
+		OPT_END(),
+	};
+
+	argc = parse_options(argc, argv, NULL, options, usage, 0);
+	if (argc != 1)
+		die("need a title for the progress output");
+	title = argv[0];
+
+	progress_testing = 1;
+	progress = start_progress(title, total);
+	while (strbuf_getline(&line, stdin) != EOF) {
+		char *end;
+
+		if (skip_prefix(line.buf, "progress ", (const char **) &end)) {
+			uint64_t item_count = strtoull(end, &end, 10);
+			if (*end != '\0')
+				die("invalid input: '%s'\n", line.buf);
+			display_progress(progress, item_count);
+		} else if (skip_prefix(line.buf, "throughput ",
+				       (const char **) &end)) {
+			uint64_t byte_count, test_ms;
+
+			byte_count = strtoull(end, &end, 10);
+			if (*end != ' ')
+				die("invalid input: '%s'\n", line.buf);
+			test_ms = strtoull(end + 1, &end, 10);
+			if (*end != '\0')
+				die("invalid input: '%s'\n", line.buf);
+			progress_test_ns = test_ms * 1000 * 1000;
+			display_throughput(progress, byte_count);
+		} else if (!strcmp(line.buf, "update"))
+			progress_test_force_update();
+		else
+			die("invalid input: '%s'\n", line.buf);
+	}
+	stop_progress(&progress);
+
+	return 0;
+}
diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c
index ce7e89028c..19ee26d931 100644
--- a/t/helper/test-tool.c
+++ b/t/helper/test-tool.c
@@ -42,6 +42,7 @@ static struct test_cmd cmds[] = {
 	{ "path-utils", cmd__path_utils },
 	{ "pkt-line", cmd__pkt_line },
 	{ "prio-queue", cmd__prio_queue },
+	{ "progress", cmd__progress },
 	{ "reach", cmd__reach },
 	{ "read-cache", cmd__read_cache },
 	{ "read-midx", cmd__read_midx },
diff --git a/t/helper/test-tool.h b/t/helper/test-tool.h
index f805bb39ae..c2aa56ef50 100644
--- a/t/helper/test-tool.h
+++ b/t/helper/test-tool.h
@@ -32,6 +32,7 @@ int cmd__parse_options(int argc, const char **argv);
 int cmd__path_utils(int argc, const char **argv);
 int cmd__pkt_line(int argc, const char **argv);
 int cmd__prio_queue(int argc, const char **argv);
+int cmd__progress(int argc, const char **argv);
 int cmd__reach(int argc, const char **argv);
 int cmd__read_cache(int argc, const char **argv);
 int cmd__read_midx(int argc, const char **argv);