t: use test_might_fail() instead of manipulating exit code manually

These tests manually coerce the exit code of invoked commands to
"success" when they don't care if the command succeeds or fails since
failure of those commands should not cause the test to fail overall.
In doing so, they intentionally break the &&-chain. Modernize by
replacing manual exit code management with test_might_fail() and a
normal &&-chain.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t1507-rev-parse-upstream.sh

@@ -123,9 +123,9 @@ test_expect_success 'checkout -b new my-side@{u} forks from the same' '
 
 test_expect_success 'merge my-side@{u} records the correct name' '
 (
-	cd clone || exit
-	git checkout master || exit
-	git branch -D new ;# can fail but is ok
+	cd clone &&
+	git checkout master &&
+	test_might_fail git branch -D new &&
 	git branch -t new my-side@{u} &&
 	git merge -s ours new@{u} &&
 	git show -s --pretty=tformat:%s >actual &&

t/t1700-split-index.sh

@@ -435,7 +435,7 @@ test_expect_success 'writing split index with null sha1 does not write cache tre
 	commit=$(git commit-tree $tree -p HEAD <msg) &&
 	git update-ref HEAD "$commit" &&
 	GIT_ALLOW_NULL_SHA1=1 git reset --hard &&
-	(test-tool dump-cache-tree >cache-tree.out || true) &&
+	test_might_fail test-tool dump-cache-tree >cache-tree.out &&
 	test_line_count = 0 cache-tree.out
 '
 

t/t4012-diff-binary.sh

@@ -102,10 +102,8 @@ test_expect_success 'apply binary patch' '
 
 test_expect_success 'diff --no-index with binary creation' '
 	echo Q | q_to_nul >binary &&
-	(: hide error code from diff, which just indicates differences
-	 git diff --binary --no-index /dev/null binary >current ||
-	 true
-	) &&
+	# hide error code from diff, which just indicates differences
+	test_might_fail git diff --binary --no-index /dev/null binary >current &&
 	rm binary &&
 	git apply --binary <current &&
 	echo Q >expected &&

t/t5400-send-pack.sh

@@ -86,7 +86,7 @@ test_expect_success 'push can be used to delete a ref' '
 test_expect_success 'refuse deleting push with denyDeletes' '
 	(
 	    cd victim &&
-	    ( git branch -D extra || : ) &&
+	    test_might_fail git branch -D extra &&
 	    git config receive.denyDeletes true &&
 	    git branch extra master
 	) &&
@@ -119,7 +119,7 @@ test_expect_success 'override denyDeletes with git -c receive-pack' '
 test_expect_success 'denyNonFastforwards trumps --force' '
 	(
 	    cd victim &&
-	    ( git branch -D extra || : ) &&
+	    test_might_fail git branch -D extra &&
 	    git config receive.denyNonFastforwards true
 	) &&
 	victim_orig=$(cd victim && git rev-parse --verify master) &&