subtree: t7900: fix 'verify one file change per commit'

As far as I can tell, this test isn't actually testing anything, because
someone forgot to tack on `--name-only` to `git log`.  This seems to
have been the case since the test was first written, back in fa16ab3
("test.sh: make sure no commit changes more than one file at a time.",
2009-04-26), unless `git log` used to do that by default and didn't need
the flag back then?

Convincing myself that it's not actually testing anything was tricky,
the code is a little hard to reason about.  It can be made a lot simpler
if instead of trying to parse all of the info from a single `git log`,
we're OK calling `git log` from inside of a loop.  And it's my opinion
that tests are not the place for clever optimized code.

So, fix and simplify the test, so that it's actually testing something
and is simpler to reason about.

Signed-off-by: Luke Shumaker <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: LukeShu

contrib/subtree/t/t7900-subtree.sh

@@ -22,33 +22,6 @@ subtree_test_create_repo () {
 	git -C "$1" config log.date relative
 }
 
-# Make sure no patch changes more than one file.
-# The original set of commits changed only one file each.
-# A multi-file change would imply that we pruned commits
-# too aggressively.
-join_commits () {
-	commit=
-	all=
-	while read x y
-	do
-		if test -z "$x"
-		then
-			continue
-		elif test "$x" = "commit:"
-		then
-			if test -n "$commit"
-			then
-				echo "$commit $all"
-				all=
-			fi
-			commit="$y"
-		else
-			all="$all $y"
-		fi
-	done
-	echo "$commit $all"
-}
-
 test_create_commit () (
 	repo=$1 &&
 	commit=$2 &&
@@ -869,19 +842,12 @@ test_expect_success 'verify one file change per commit' '
 		cd "$test_count" &&
 		git subtree split --prefix="sub dir2" --branch subproj2-br &&
 
-		x= &&
-		git log --pretty=format:"commit: %H" | join_commits |
-		(
-			while read commit a b
-			do
-				test_debug "echo Verifying commit $commit"
-				test_debug "echo a: $a"
-				test_debug "echo b: $b"
-				test "$b" = ""
-				x=1
-			done
-			test "$x" = 1
-		)
+		git log --format="%H" >commit-list &&
+		while read commit
+		do
+			git log -n1 --format="" --name-only "$commit" >file-list &&
+			test_line_count -le 1 file-list || return 1
+		done <commit-list
 	)
 '