diff --git a/t/t3311-notes-merge-fanout.sh b/t/t3311-notes-merge-fanout.sh
index 93516ef67c..37151a3adc 100755
--- a/t/t3311-notes-merge-fanout.sh
+++ b/t/t3311-notes-merge-fanout.sh
@@ -114,12 +114,12 @@ cp expect_log_x expect_log_y
 test_expect_success 'Add a few hundred commits w/notes to trigger fanout (x -> y)' '
 	git update-ref refs/notes/y refs/notes/x &&
 	git config core.notesRef refs/notes/y &&
-	i=5 &&
-	while test $i -lt $num
+	test_commit_bulk --start=6 --id=commit $((num - 5)) &&
+	i=0 &&
+	while test $i -lt $((num - 5))
 	do
-		i=$(($i + 1)) &&
-		test_commit "commit$i" >/dev/null &&
-		git notes add -m "notes for commit$i" || return 1
+		git notes add -m "notes for commit$i" HEAD~$i || return 1
+		i=$((i + 1))
 	done &&
 	test "$(git rev-parse refs/notes/y)" != "$(git rev-parse refs/notes/x)" &&
 	# Expected number of commits and notes
diff --git a/t/t5310-pack-bitmaps.sh b/t/t5310-pack-bitmaps.sh
index a26c8ba9a2..6640329ebf 100755
--- a/t/t5310-pack-bitmaps.sh
+++ b/t/t5310-pack-bitmaps.sh
@@ -21,15 +21,9 @@ has_any () {
 }
 
 test_expect_success 'setup repo with moderate-sized history' '
-	for i in $(test_seq 1 10)
-	do
-		test_commit $i
-	done &&
+	test_commit_bulk --id=file 100 &&
 	git checkout -b other HEAD~5 &&
-	for i in $(test_seq 1 10)
-	do
-		test_commit side-$i
-	done &&
+	test_commit_bulk --id=side 10 &&
 	git checkout master &&
 	bitmaptip=$(git rev-parse master) &&
 	blob=$(echo tagged-blob | git hash-object -w --stdin) &&
@@ -106,10 +100,7 @@ test_expect_success 'clone from bitmapped repository' '
 '
 
 test_expect_success 'setup further non-bitmapped commits' '
-	for i in $(test_seq 1 10)
-	do
-		test_commit further-$i
-	done
+	test_commit_bulk --id=further 10
 '
 
 rev_list_tests 'partial bitmap'
diff --git a/t/t5702-protocol-v2.sh b/t/t5702-protocol-v2.sh
index 5b33f625dd..011b81d4fc 100755
--- a/t/t5702-protocol-v2.sh
+++ b/t/t5702-protocol-v2.sh
@@ -499,10 +499,7 @@ test_expect_success 'upload-pack respects client shallows' '
 
 	# Add extra commits to the client so that the whole fetch takes more
 	# than 1 request (due to negotiation)
-	for i in $(test_seq 1 32)
-	do
-		test_commit -C client c$i
-	done &&
+	test_commit_bulk -C client --id=c 32 &&
 
 	git -C server checkout -b newbranch base &&
 	test_commit -C server client_wants &&
@@ -711,10 +708,7 @@ test_expect_success 'when server does not send "ready", expect FLUSH' '
 	# Create many commits to extend the negotiation phase across multiple
 	# requests, so that the server does not send "ready" in the first
 	# request.
-	for i in $(test_seq 1 32)
-	do
-		test_commit -C http_child c$i
-	done &&
+	test_commit_bulk -C http_child --id=c 32 &&
 
 	# After the acknowledgments section, pretend that a DELIM
 	# (0001) was sent instead of a FLUSH (0000).
diff --git a/t/t5703-upload-pack-ref-in-want.sh b/t/t5703-upload-pack-ref-in-want.sh
index 0951d1bbdc..de4b6106ef 100755
--- a/t/t5703-upload-pack-ref-in-want.sh
+++ b/t/t5703-upload-pack-ref-in-want.sh
@@ -176,7 +176,7 @@ test_expect_success 'setup repos for change-while-negotiating test' '
 		git clone "http://127.0.0.1:$LIB_HTTPD_PORT/smart/repo" "$LOCAL_PRISTINE" &&
 		cd "$LOCAL_PRISTINE" &&
 		git checkout -b side &&
-		for i in $(test_seq 1 33); do test_commit s$i; done &&
+		test_commit_bulk --id=s 33 &&
 
 		# Add novel commits to upstream
 		git checkout master &&
@@ -287,7 +287,7 @@ test_expect_success 'setup repos for fetching with ref-in-want tests' '
 		git clone "file://$REPO" "$LOCAL_PRISTINE" &&
 		cd "$LOCAL_PRISTINE" &&
 		git checkout -b side &&
-		for i in $(test_seq 1 33); do test_commit s$i; done &&
+		test_commit_bulk --id=s 33 &&
 
 		# Add novel commits to upstream
 		git checkout master &&
diff --git a/t/t6200-fmt-merge-msg.sh b/t/t6200-fmt-merge-msg.sh
index 93f23cfa82..8a72b4c43a 100755
--- a/t/t6200-fmt-merge-msg.sh
+++ b/t/t6200-fmt-merge-msg.sh
@@ -66,12 +66,7 @@ test_expect_success setup '
 	git commit -a -m "Right #5" &&
 
 	git checkout -b long &&
-	i=0 &&
-	while test $i -lt 30
-	do
-		test_commit $i one &&
-		i=$(($i+1))
-	done &&
+	test_commit_bulk --start=0 --message=%s --filename=one 30 &&
 
 	git show-branch &&
 
diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index 27b81276fc..d4f199391f 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -233,6 +233,129 @@ test_merge () {
 	git tag "$1"
 }
 
+# Efficiently create <nr> commits, each with a unique number (from 1 to <nr>
+# by default) in the commit message.
+#
+# Usage: test_commit_bulk [options] <nr>
+#   -C <dir>:
+#	Run all git commands in directory <dir>
+#   --ref=<n>:
+#	ref on which to create commits (default: HEAD)
+#   --start=<n>:
+#	number commit messages from <n> (default: 1)
+#   --message=<msg>:
+#	use <msg> as the commit mesasge (default: "commit %s")
+#   --filename=<fn>:
+#	modify <fn> in each commit (default: %s.t)
+#   --contents=<string>:
+#	place <string> in each file (default: "content %s")
+#   --id=<string>:
+#	shorthand to use <string> and %s in message, filename, and contents
+#
+# The message, filename, and contents strings are evaluated by printf, with the
+# first "%s" replaced by the current commit number. So you can do:
+#
+#   test_commit_bulk --filename=file --contents="modification %s"
+#
+# to have every commit touch the same file, but with unique content.
+#
+test_commit_bulk () {
+	tmpfile=.bulk-commit.input
+	indir=.
+	ref=HEAD
+	n=1
+	message='commit %s'
+	filename='%s.t'
+	contents='content %s'
+	while test $# -gt 0
+	do
+		case "$1" in
+		-C)
+			indir=$2
+			shift
+			;;
+		--ref=*)
+			ref=${1#--*=}
+			;;
+		--start=*)
+			n=${1#--*=}
+			;;
+		--message=*)
+			message=${1#--*=}
+			;;
+		--filename=*)
+			filename=${1#--*=}
+			;;
+		--contents=*)
+			contents=${1#--*=}
+			;;
+		--id=*)
+			message="${1#--*=} %s"
+			filename="${1#--*=}-%s.t"
+			contents="${1#--*=} %s"
+			;;
+		-*)
+			BUG "invalid test_commit_bulk option: $1"
+			;;
+		*)
+			break
+			;;
+		esac
+		shift
+	done
+	total=$1
+
+	add_from=
+	if git -C "$indir" rev-parse --verify "$ref"
+	then
+		add_from=t
+	fi
+
+	while test "$total" -gt 0
+	do
+		test_tick &&
+		echo "commit $ref"
+		printf 'author %s <%s> %s\n' \
+			"$GIT_AUTHOR_NAME" \
+			"$GIT_AUTHOR_EMAIL" \
+			"$GIT_AUTHOR_DATE"
+		printf 'committer %s <%s> %s\n' \
+			"$GIT_COMMITTER_NAME" \
+			"$GIT_COMMITTER_EMAIL" \
+			"$GIT_COMMITTER_DATE"
+		echo "data <<EOF"
+		printf "$message\n" $n
+		echo "EOF"
+		if test -n "$add_from"
+		then
+			echo "from $ref^0"
+			add_from=
+		fi
+		printf "M 644 inline $filename\n" $n
+		echo "data <<EOF"
+		printf "$contents\n" $n
+		echo "EOF"
+		echo
+		n=$((n + 1))
+		total=$((total - 1))
+	done >"$tmpfile"
+
+	git -C "$indir" \
+	    -c fastimport.unpacklimit=0 \
+	    fast-import <"$tmpfile" || return 1
+
+	# This will be left in place on failure, which may aid debugging.
+	rm -f "$tmpfile"
+
+	# If we updated HEAD, then be nice and update the index and working
+	# tree, too.
+	if test "$ref" = "HEAD"
+	then
+		git -C "$indir" checkout -f HEAD || return 1
+	fi
+
+}
+
 # This function helps systems where core.filemode=false is set.
 # Use it instead of plain 'chmod +x' to set or unset the executable bit
 # of a file in the working directory and add it to the index.