Re: [PATCH v3 1/4] test-lib-functions: introduce test_line_count_cmd

checking number of lines of text in the stdout of a command.
One of such examples is t6400, that checks number of files
in various states.

Some of those commands are Git command, and we would like to check
their exit status.  In some of those checks, we pipe the stdout of
those commands to "wc -l" to count the number lines, thus losing
the exit status.

Introduce a helper function to check for the number of lines in stdout
from those commands.

This helper will create a temporary file in the process, thus it may
affect the output of some checks.

Signed-off-by: Đoàn Trần Công Danh <redacted>
---
  t/test-lib-functions.sh | 80 +++++++++++++++++++++++++++++++++++++++++
  1 file changed, 80 insertions(+)

diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index f0448daa74..e055a4f808 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh

@@ -845,6 +845,86 @@ test_line_count () {
  	fi
  }
  
+# test_line_count_cmd checks the exit status, and the number of lines in
+# the captured stdout of a command.
+#
+# SYNOPSIS:
+#
+#	test_line_count_cmd <binop> <value> [!] cmd [args...]
+#
+# Expect succeed exit status when running
+#
+#	cmd [args...]
+#
+# then, run sh's "test <# of lines in stdout> <binop> <value>"
+#
+# OPTIONS:
+# !:
+#	Instead of expecting "cmd [args...]" succeed, expect its failure.
+#	Note, if the command under testing is "git",
+#	test_must_fail should be used instead of "!".
+#
+# EXAMPLE:
+#	test_line_count_cmd -ge 10 git tag --no-contains v1.0.0
+#	test_line_count_cmd -le 10 ! grep some-text a-file
+#	test_line_count_cmd = 0 test_must_fail git rev-parse --verify abcd1234
+#
+# NOTE:
+# * a temporary file named test_line_count_cmd_.out will be created under
+# $TRASH_DIRECTORY/.git/trash iff $TRASH_DIRECTORY/.git/ exists.
+# Otherwise, created in $TRASH_DIRECTORY. This temporary file will be
+# cleaned by test_when_finished
+test_line_count_cmd () {
+	{
+		local outop outval outfile
+		local expect_failure actual_failure
+		local trashdir="$TRASH_DIRECTORY"
+
+		if test -d "$TRASH_DIRECTORY/.git"
+		then
+			trashdir="$TRASH_DIRECTORY/.git/trash" &&
+			mkdir -p "$trashdir"
+		fi &&
+		if test $# -lt 3
+		then
+			BUG "missing <binary-ops> and <value>"

+		fi &&
+		outop="$1" &&
+		outval="$2" &&
+		shift 2 &&
+		outfile="$trashdir/test_line_count_cmd_.out" &&
+		if test "x$1" = "x!"
+		then
+			shift &&
+			expect_failure=yes
+		fi &&
+		if test $# = 0
+		then
+			BUG "test_line_count_cmd: no command to be run"
+		else
+			test_when_finished "rm -f '$outfile'" &&
+			exec 8>"$outfile"
+			# We need to redirect stderr to &9,
+			# and redirect this function's 9>&2
+			# in order to not messed with -x
+			if ! "$@" >&8 2>&9
+			then
+				actual_failure=yes
+			fi
+		fi 8>&1 &&
+		case "$expect_failure,$actual_failure" in
+		yes,)
+			echo >&4 "error: '$@' succeed!" &&

+			return 1
+			;;
+		,yes)
+			echo >&4 "error: '$@' run into failure!" &&
+			return 1
+		esac &&

+		test_line_count "$outop" "$outval" "$outfile" >&4
+	} 9>&2 2>&4
+}
+
  test_file_size () {
  	test "$#" -ne 1 && BUG "1 param"
  	test-tool path-utils file-size "$1"