diff --git a/tests/base64decode.sh b/tests/base64decode.sh
index eef96fe..a0c656c 100755
--- a/tests/base64decode.sh
+++ b/tests/base64decode.sh
@@ -1,23 +1,26 @@
-#!/usr/bin/env bash
+#!/bin/sh
 
 input=$(mktemp)
 binary=$(mktemp)
 
-trap "rm -f $input $binary" EXIT
+trap 'rm -f "$input" "$binary"' 0
 
-function sseq()
+sseq()
 {
-	for ((i = $1; i < $2; i=i<<1)); do
-		echo $i
+	i=$1
+	limit=$2
+	while [ "$i" -lt "$limit" ]; do
+		echo "$i"
+		i=$((i << 1))
 	done
 }
 
-function do_base64()
+do_base64()
 {
-	if [ -n "$(type -p base64)" ]; then
-		base64 $1
-	elif [ -n "$(type -p uuencode)" ]; then
-		uuencode -m $1 data | sed 1d | sed '$d'
+	if command -v base64 >/dev/null 2>&1; then
+		base64 "$1"
+	elif command -v uuencode >/dev/null 2>&1; then
+		uuencode -m "$1" data | sed 1d | sed '$d'
 	else
 		echo "No tool found for base64 encoding." >&2
 		exit 1
@@ -26,13 +29,10 @@ function do_base64()
 
 for i in $(sseq 1 1024) 2048 10240;
 do
-	echo $i
-	dd if=/dev/urandom of=$binary bs=1 count=$i &>/dev/null
-	echo "-----BEGIN INITSTATE-----" > $input
-	do_base64 $binary >> $input
-	echo "-----END INITSTATE-----" >> $input
-	./base64decode $input $binary
-	if [ $? -ne 0 ]; then
-		exit 1
-	fi
+	echo "$i"
+	dd if=/dev/urandom of="$binary" bs=1 count="$i" >/dev/null 2>&1
+	echo "-----BEGIN INITSTATE-----" > "$input"
+	do_base64 "$binary" >> "$input"
+	echo "-----END INITSTATE-----" >> "$input"
+	./base64decode "$input" "$binary" || exit 1
 done
diff --git a/tests/common b/tests/common
index 11e2548..c03f822 100644
--- a/tests/common
+++ b/tests/common
@@ -3,12 +3,15 @@
 # Get the size of a file in bytes
 #
 # @1: filename
-function get_filesize()
+get_filesize()
 {
-	if [[ "$(uname -s)" =~ (Linux|CYGWIN_NT-|GNU) ]]; then
-		stat -c%s "$1"
-	else
-		# OpenBSD
-		stat -f%z "$1"
-	fi
+	case "$(uname -s)" in
+		Linux|CYGWIN_NT-*|GNU)
+			stat -c%s "$1"
+			;;
+		*)
+			# OpenBSD
+			stat -f%z "$1"
+			;;
+	esac
 }
diff --git a/tests/fuzz.sh b/tests/fuzz.sh
index 5e21c37..ebe1b80 100755
--- a/tests/fuzz.sh
+++ b/tests/fuzz.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 
 TESTDIR=${abs_top_testdir:-$(dirname "$0")}
 DIR=${PWD}
@@ -12,8 +12,8 @@ while :; do
   echo "Passing test cases $l to $((l + MAXLINES))"
   tmp=$(echo "${corpus}" | sed -n "${l},$((l + MAXLINES))p")
   [ -z "${tmp}" ] && exit 0
-  ${DIR}/fuzz ${tmp}
+  "${DIR}/fuzz" ${tmp}
   rc=$?
-  [ $rc -ne 0 ] && exit $rc
+  [ "$rc" -ne 0 ] && exit "$rc"
   l=$((l + MAXLINES))
 done
diff --git a/tests/oss-fuzz.sh b/tests/oss-fuzz.sh
index ba65c8c..b00eed0 100755
--- a/tests/oss-fuzz.sh
+++ b/tests/oss-fuzz.sh
@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/bin/sh
 
 set -ex
 
@@ -8,20 +8,21 @@ export WORK=${WORK:-$(pwd)}
 export OUT=${OUT:-$(pwd)/out}
 CFLAGS="${CFLAGS} -fno-sanitize=bounds"  # due to casts to Crypt_Int*
 
-mkdir -p $OUT
+mkdir -p "$OUT"
 
 build=$WORK/build
-rm -rf $build
-mkdir -p $build
+rm -rf "$build"
+mkdir -p "$build"
 
 export LIBTPMS=$(pwd)
 autoreconf -vfi
 
-cd $build
-$LIBTPMS/configure --disable-shared --enable-static --with-openssl --with-tpm2
-make -j$(nproc) && make -C tests fuzz
+cd "$build"
+"$LIBTPMS"/configure --disable-shared --enable-static --with-openssl --with-tpm2
+jobs=$(getconf _NPROCESSORS_ONLN 2>/dev/null || echo 1)
+make -j"$jobs" && make -C tests fuzz
 
 zip -jqr $OUT/fuzz_seed_corpus.zip "$LIBTPMS/tests/corpus-execute-command"
 
-find $build -type f -executable -name "fuzz*" -exec mv {} $OUT \;
-find $build -type f -name "*.options" -exec mv {} $OUT \;
+find "$build" -type f -executable -name "fuzz*" -exec mv {} "$OUT" \;
+find "$build" -type f -name "*.options" -exec mv {} "$OUT" \;
diff --git a/tests/run-fuzzer.sh b/tests/run-fuzzer.sh
index 0a86c63..2d47f46 100755
--- a/tests/run-fuzzer.sh
+++ b/tests/run-fuzzer.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 
 # For the license, see the LICENSE file in the root directory.
 
@@ -6,18 +6,19 @@ DIR=${PWD}/$(dirname "$0")
 ROOT=${DIR}/..
 WORKDIR=$(mktemp -d)
 
-function cleanup()
+cleanup()
 {
-	rm -rf ${WORKDIR}
+	rm -rf "${WORKDIR}"
 }
 
-trap "cleanup" QUIT EXIT
+trap 'cleanup' 0 3
 
-pushd $WORKDIR
+oldpwd=$(pwd)
+cd "$WORKDIR" || exit 1
 
-${DIR}/fuzz $@ ${DIR}/corpus-execute-command
+"${DIR}/fuzz" "$@" "${DIR}/corpus-execute-command"
 rc=$?
 
-popd
+cd "$oldpwd" || exit 1
 
 exit $rc
diff --git a/tests/tpm2_createprimary.sh b/tests/tpm2_createprimary.sh
index 9b24848..7796d59 100755
--- a/tests/tpm2_createprimary.sh
+++ b/tests/tpm2_createprimary.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 
 # For the license, see the LICENSE file in the root directory.
 
diff --git a/tests/tpm2_cve-2023-1017.sh b/tests/tpm2_cve-2023-1017.sh
index 662b090..86dd001 100755
--- a/tests/tpm2_cve-2023-1017.sh
+++ b/tests/tpm2_cve-2023-1017.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 
 # For the license, see the LICENSE file in the root directory.
 
diff --git a/tests/tpm2_cve-2023-1018.sh b/tests/tpm2_cve-2023-1018.sh
index debe2e7..69abcfb 100755
--- a/tests/tpm2_cve-2023-1018.sh
+++ b/tests/tpm2_cve-2023-1018.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 
 # For the license, see the LICENSE file in the root directory.
 
diff --git a/tests/tpm2_pcr_read.sh b/tests/tpm2_pcr_read.sh
index fcd8858..24c9281 100755
--- a/tests/tpm2_pcr_read.sh
+++ b/tests/tpm2_pcr_read.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 
 # For the license, see the LICENSE file in the root directory.
 
diff --git a/tests/tpm2_run_test.sh b/tests/tpm2_run_test.sh
index 2f5437a..f0b3732 100755
--- a/tests/tpm2_run_test.sh
+++ b/tests/tpm2_run_test.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 
 # For the license, see the LICENSE file in the root directory.
 
@@ -10,20 +10,22 @@ WORKDIR=$(mktemp -d)
 
 . "${TESTDIR}/common"
 
-function cleanup()
+cleanup()
 {
 	rm -rf "${WORKDIR}"
 }
 
-trap "cleanup" QUIT EXIT
+trap 'cleanup' 0 3
 
-pushd "$WORKDIR" &>/dev/null || exit 1
+oldpwd=$(pwd)
+cd "$WORKDIR" || exit 1
 
 "${DIR}/${1}"
 rc=$?
 
 if ! fs=$(get_filesize NVChip); then
-	exit 1
+		cd "$oldpwd" || exit 1
+		exit 1
 fi
 exp=176832
 if [ "$fs" -ne "$exp" ]; then
@@ -33,6 +35,6 @@ if [ "$fs" -ne "$exp" ]; then
 	rc=1
 fi
 
-popd &>/dev/null || exit 1
+cd "$oldpwd" || exit 1
 
 exit $rc
diff --git a/tests/tpm2_selftest.sh b/tests/tpm2_selftest.sh
index d06e2ee..22504e5 100755
--- a/tests/tpm2_selftest.sh
+++ b/tests/tpm2_selftest.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 
 # For the license, see the LICENSE file in the root directory.
 
diff --git a/tests/tpm2_setprofile.sh b/tests/tpm2_setprofile.sh
index 88c6f52..8e77618 100755
--- a/tests/tpm2_setprofile.sh
+++ b/tests/tpm2_setprofile.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 
 # For the license, see the LICENSE file in the root directory.
 
@@ -10,20 +10,22 @@ WORKDIR=$(mktemp -d)
 
 . "${TESTDIR}/common"
 
-function cleanup()
+cleanup()
 {
 	rm -rf "${WORKDIR}"
 }
 
-trap "cleanup" QUIT EXIT
+trap 'cleanup' 0 3
 
-pushd "$WORKDIR" &>/dev/null || exit 1
+oldpwd=$(pwd)
+cd "$WORKDIR" || exit 1
 
 "${DIR}/tpm2_setprofile"
 rc=$?
 
 if ! fs=$(get_filesize NVChip); then
-	exit 1
+		cd "$oldpwd" || exit 1
+		exit 1
 fi
 exp=176832
 if [ "$fs" -ne "$exp" ]; then
@@ -33,6 +35,6 @@ if [ "$fs" -ne "$exp" ]; then
 	rc=1
 fi
 
-popd &>/dev/null || exit 1
+cd "$oldpwd" || exit 1
 
 exit "$rc"