[RFC PATCH 5/6] test-lib: add run_and_check_trace2

[Derrick Stolee <stolee@gmail.com>]

The trace2 facility allows tracing category-key-value triples that
we can use to communicate runtime information to a side channel.
One use is to track the number of commits that are walked by a
graph algorithm.

Add run_and_check_trace2 test function to run a given command with
GIT_TR2_PERFORMANCE running. Then, check the output for the
expected category-key-value triple.

Use this function in t6600-test-reach.sh to verify can_all_from_reach
only visits 11 commits in the example.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 t/t6600-test-reach.sh |  6 ++++++
 t/test-lib.sh         | 14 ++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/t/t6600-test-reach.sh b/t/t6600-test-reach.sh
index d139a00d1d..98ad25bb45 100755
--- a/t/t6600-test-reach.sh
+++ b/t/t6600-test-reach.sh
@@ -183,6 +183,12 @@ test_expect_success 'can_all_from_reach:hit' '
 	test_three_modes can_all_from_reach
 '
 
+test_expect_success 'can_all_from_reach:perf' '
+	cp commit-graph-full .git/objects/info/commit-graph &&
+	run_and_check_trace2 can_all_from_reach_with_flag num_walked 40 input \
+		"test-tool reach can_all_from_reach"
+'
+
 test_expect_success 'can_all_from_reach:miss' '
 	cat >input <<-\EOF &&
 	X:commit-2-10
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 8bb0f4348e..9b9f68f324 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1231,3 +1231,17 @@ test_lazy_prereq CURL '
 test_lazy_prereq SHA1 '
 	test $(git hash-object /dev/null) = e69de29bb2d1d6434b8b29ae775ad8c2e48c5391
 '
+
+# Useage: run_and_check_trace2 <category> <key> <value> <file> <command>
+# Run "command <file" with GIT_TR2_PERFORMANCE logging to a file and
+# check that file for a data output matching category.key = value.
+run_and_check_trace2 () {
+	CATEGORY=$1
+	KEY=$2
+	VALUE=$3
+	INPUT=$4
+	COMMAND=$5
+	# GIT_TR2_PERFORMANCE="$(pwd)/perf-log.txt"
+	GIT_TR2_PERFORMANCE="$(pwd)/perf-log.txt" $COMMAND <$INPUT &&
+	cat perf-log.txt | grep "category:$CATEGORY key:$KEY value:$VALUE"
+}
-- 
2.19.0.rc2