[GSOC][PATCH v4] t3701: don't lose "git" exit codes in test scripts

[Edwin Fernando <edwinfernando734@gmail.com>]

Exit codes are lost due to piping: "git ... | <command>"
Fix these issues using the intermediate step of writing output to file.

Signed-off-by: Edwin Fernando <edwinfernando734@gmail.com>
---
Apply my changes on top of the latest commit in upstream history.
Test 76 in t3701 fails. This commit breaks the test:
a9f4a01760 (Merge branch 'jk/add-p-unmerged-fix', 2023-03-19)
Identified by checking out commits in:
"git log --oneline -- t/t3701-add-interactive.sh"
I don't know if it is normal to have broken tests in the main repository.

 t/t3701-add-interactive.sh | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/t/t3701-add-interactive.sh b/t/t3701-add-interactive.sh
index 3982b6b49d..b8291206a0 100755
--- a/t/t3701-add-interactive.sh
+++ b/t/t3701-add-interactive.sh
@@ -286,8 +286,10 @@ test_expect_success FILEMODE 'patch does not affect mode' '
 	echo content >>file &&
 	chmod +x file &&
 	printf "n\\ny\\n" | git add -p &&
-	git show :file | grep content &&
-	git diff file | grep "new mode"
+	git show :file >show &&
+	grep content show &&
+	git diff file >diff &&
+	grep "new mode" diff
 '
 
 test_expect_success FILEMODE 'stage mode but not hunk' '
@@ -295,8 +297,10 @@ test_expect_success FILEMODE 'stage mode but not hunk' '
 	echo content >>file &&
 	chmod +x file &&
 	printf "y\\nn\\n" | git add -p &&
-	git diff --cached file | grep "new mode" &&
-	git diff          file | grep "+content"
+	git diff --cached file >diff &&
+	grep "new mode" diff &&
+	git diff file >diff &&
+	grep "+content" diff
 '
 
 
-- 
2.40.0