t: fix &&-chaining issues around setup which might fail

Many tests have an initial setup step that might fail based
on whether earlier tests in the script have succeeded or
not. Using a trick like "|| true" breaks the &&-chain,
missing earlier failures (and fooling --chain-lint).

We can use test_might_fail in some cases, which is correct
and makes the intent more obvious. We can also use
test_unconfig for unsetting config (and which is more
robust, as well).

The case in t9500 is an oddball. It wants to run cmd1 _or_
cmd2, and does it like:

  cmd1 || cmd2 &&
  other_stuff

It's not wrong in this case, but it's a bad habit to get
into, because it breaks the &&-chain if used anywhere except
at the beginning of the test (and we use the correct
solution here, putting it inside a block for precedence).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5503-tagfollow.sh

@@ -139,8 +139,8 @@ EOF
 '
 
 test_expect_success 'new clone fetch master and tags' '
-	git branch -D cat
-	rm -f $U
+	test_might_fail git branch -D cat &&
+	rm -f $U &&
 	(
 		mkdir clone2 &&
 		cd clone2 &&

t/t6032-merge-large-rename.sh

@@ -28,10 +28,10 @@ make_text() {
 
 test_rename() {
 	test_expect_success "rename ($1, $2)" '
-	n='$1'
-	expect='$2'
+	n='$1' &&
+	expect='$2' &&
 	git checkout -f master &&
-	git branch -D test$n || true &&
+	test_might_fail git branch -D test$n &&
 	git reset --hard initial &&
 	for i in $(count $n); do
 		make_text $i initial initial >$i

t/t7201-co.sh

@@ -591,7 +591,7 @@ test_expect_success 'checkout --conflict=merge, overriding config' '
 '
 
 test_expect_success 'checkout --conflict=diff3' '
-	git config --unset merge.conflictstyle
+	test_unconfig merge.conflictstyle &&
 	setup_conflicting_index &&
 	echo "none of the above" >sample &&
 	echo ourside >expect &&

t/t7508-status.sh

@@ -538,7 +538,7 @@ A  dir2/added
 ?? untracked
 EOF
 test_expect_success 'status -s -uall' '
-	git config --unset status.showuntrackedfiles
+	test_unconfig status.showuntrackedfiles &&
 	git status -s -uall >output &&
 	test_cmp expect output
 '

t/t9500-gitweb-standalone-no-errors.sh

@@ -779,7 +779,10 @@ test_expect_success \
 
 test_expect_success \
 	'unborn HEAD: "summary" page (with "heads" subview)' \
-	'git checkout orphan_branch || git checkout --orphan orphan_branch &&
+	'{
+		git checkout orphan_branch ||
+		git checkout --orphan orphan_branch
+	 } &&
 	 test_when_finished "git checkout master" &&
 	 gitweb_run "p=.git;a=summary"'