diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index a4c94e4..9ef4fb9 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -23,7 +23,7 @@
 set -eu
 
 if [ -d library -a -d include -a -d tests ]; then :; else
-    echo "Must be run from mbed TLS root" >&2
+    err_msg "Must be run from mbed TLS root"
     exit 1
 fi
 
@@ -31,19 +31,30 @@
 CONFIG_BAK="$CONFIG_H.bak"
 
 MEMORY=0
-SHORT=0
 FORCE=0
 
+# Default commands, can be overriden by the environment
+: ${OPENSSL:="openssl"}
+: ${OPENSSL_LEGACY:="$OPENSSL"}
+: ${GNUTLS_CLI:="gnutls-cli"}
+: ${GNUTLS_SERV:="gnutls-serv"}
+: ${GNUTLS_LEGACY_CLI:="$GNUTLS_CLI"}
+: ${GNUTLS_LEGACY_SERV:="$GNUTLS_SERV"}
 : ${OUT_OF_SOURCE_DIR:=./mbedtls_out_of_source_build}
 
 usage()
 {
-    echo "Usage: $0"
-    echo -e "  -h|--help\t\tPrint this help."
-    echo -e "  -m|--memory\t\tAdditional optional memory tests."
-    echo -e "  -s|--short\t\tSubset of tests."
-    echo -e "  -f|--force\t\tForce the tests to overwrite any modified files."
-    echo -e "  --out-of-source-dir\t\tDirectory used for CMake out-of-source build tests."
+    printf "Usage: $0\n"
+    printf "  -h|--help\t\tPrint this help.\n"
+    printf "  -m|--memory\t\tAdditional optional memory tests.\n"
+    printf "  -f|--force\t\tForce the tests to overwrite any modified files.\n"
+    printf "     --out-of-source-dir\t\tDirectory used for CMake out-of-source build tests."
+    printf "     --openssl=<OpenSSL_path>\t\tPath to OpenSSL executable to use for most tests.\n"
+    printf "     --openssl-legacy=<OpenSSL_path>\t\tPath to OpenSSL executable to use for legacy tests e.g. SSLv3.\n"
+    printf "     --gnutls-cli=<GnuTLS_cli_path>\t\tPath to GnuTLS client executable to use for most tests.\n"
+    printf "     --gnutls-serv=<GnuTLS_serv_path>\t\tPath to GnuTLS server executable to use for most tests.\n"
+    printf "     --gnutls-legacy-cli=<GnuTLS_cli_path>\t\tPath to GnuTLS client executable to use for legacy tests.\n"
+    printf "     --gnutls-legacy-serv=<GnuTLS_serv_path>\t\tPath to GnuTLS server executable to use for legacy tests.\n"
 }
 
 # remove built files as well as the cmake cache/config
@@ -72,14 +83,26 @@
     echo "******************************************************************"
 }
 
+err_msg()
+{
+    echo "$1" >&2
+}
+
+check_tools()
+{
+    for TOOL in "$@"; do
+        if ! `hash "$TOOL" >/dev/null 2>&1`; then
+            err_msg "$TOOL not found!"
+            exit 1
+        fi
+    done
+}
+
 while [ $# -gt 0 ]; do
     case "$1" in
         --memory|-m*)
             MEMORY=${1#-m}
             ;;
-        --short|-s)
-            SHORT=1
-            ;;
         --force|-f)
             FORCE=1
             ;;
@@ -87,8 +110,32 @@
             shift
             OUT_OF_SOURCE_DIR="$1"
             ;;
+        --openssl)
+            shift
+            OPENSSL="$1"
+            ;;
+        --openssl-legacy)
+            shift
+            OPENSSL_LEGACY="$1"
+            ;;
+        --gnutls-cli)
+            shift
+            GNUTLS_CLI="$1"
+            ;;
+        --gnutls-serv)
+            shift
+            GNUTLS_SERV="$1"
+            ;;
+        --gnutls-legacy-cli)
+            shift
+            GNUTLS_LEGACY_CLI="$1"
+            ;;
+        --gnutls-legacy-serv)
+            shift
+            GNUTLS_LEGACY_SERV="$1"
+            ;;
         --help|-h|*)
-            usage()
+            usage
             exit 1
             ;;
     esac
@@ -102,7 +149,7 @@
 else
 
     if [ -d yotta/module ]; then
-        echo "Warning - there is an existing yotta module in the directory 'yotta/module'" >&2
+        err_msg "Warning - there is an existing yotta module in the directory 'yotta/module'"
         echo "You can either delete your work and retry, or force the test to overwrite the"
         echo "test by rerunning the script as: $0 --force"
         exit 1
@@ -117,13 +164,28 @@
 
     if ! git diff-files --quiet include/mbedtls/config.h; then
         echo $?
-        echo "Warning - the configuration file 'include/mbedtls/config.h' has been edited. " >&2
+        err_msg "Warning - the configuration file 'include/mbedtls/config.h' has been edited. "
         echo "You can either delete or preserve your work, or force the test by rerunning the"
         echo "script as: $0 --force"
         exit 1
     fi
 fi
 
+msg "info: $0 configuration"
+echo "MEMORY: $MEMORY"
+echo "FORCE: $FORCE"
+echo "OPENSSL: $OPENSSL"
+echo "OPENSSL_LEGACY: $OPENSSL_LEGACY"
+echo "GNUTLS_CLI: $GNUTLS_CLI"
+echo "GNUTLS_SERV: $GNUTLS_SERV"
+echo "GNUTLS_LEGACY_CLI: $GNUTLS_LEGACY_CLI"
+echo "GNUTLS_LEGACY_SERV: $GNUTLS_LEGACY_SERV"
+
+# Make sure the tools we need are available.
+check_tools "$OPENSSL" "$OPENSSL_LEGACY" "$GNUTLS_CLI" "$GNUTLS_SERV" \
+    "$GNUTLS_LEGACY_CLI" "$GNUTLS_LEGACY_SERV" "doxygen" "dot" \
+    "arm-none-eabi-gcc" "armcc"
+
 #
 # Test Suites to be executed
 #
@@ -136,7 +198,9 @@
 # Indicative running times are given for reference.
 
 msg "info: output_env.sh"
-scripts/output_env.sh
+OPENSSL="$OPENSSL" OPENSSL_LEGACY="$OPENSSL_LEGACY" GNUTLS_CLI="$GNUTLS_CLI" \
+    GNUTLS_SERV="$GNUTLS_SERV" GNUTLS_LEGACY_CLI="$GNUTLS_LEGACY_CLI" \
+    GNUTLS_LEGACY_SERV="$GNUTLS_LEGACY_SERV" scripts/output_env.sh
 
 msg "test: recursion.pl" # < 1s
 tests/scripts/recursion.pl library/*.c
@@ -151,11 +215,9 @@
 cleanup
 tests/scripts/check-names.sh
 
-if which doxygen >/dev/null; then
-    msg "test: doxygen warnings" # ~ 3s
-    cleanup
-    tests/scripts/doxygen.sh
-fi
+msg "test: doxygen warnings" # ~ 3s
+cleanup
+tests/scripts/doxygen.sh
 
 msg "build: create and build yotta module" # ~ 30s
 cleanup
@@ -175,13 +237,6 @@
 msg "test/build: ref-configs (ASan build)" # ~ 6 min 20s
 tests/scripts/test-ref-configs.pl
 
-# Most frequent issues are likely to be caught at this point
-if [ $SHORT -eq 1 ]; then
-    msg "Done, cleaning up"
-    cleanup
-    exit 0
-fi
-
 msg "build: with ASan (rebuild after ref-configs)" # ~ 1 min
 make
 
@@ -199,7 +254,8 @@
 make test
 
 msg "build: SSLv3 - compat.sh (ASan build)" # ~ 6 min
-tests/compat.sh -m 'ssl3 tls1 tls1_1 tls1_2 dtls1 dtls1_2'
+tests/compat.sh -m 'tls1 tls1_1 tls1_2 dtls1 dtls1_2'
+OPENSSL_CMD="$OPENSSL_LEGACY" tests/compat.sh -m 'ssl3'
 
 msg "build: SSLv3 - ssl-opt.sh (ASan build)" # ~ 6 min
 tests/ssl-opt.sh
@@ -219,7 +275,7 @@
 tests/ssl-opt.sh -f Default
 
 msg "test: compat.sh RC4, DES & NULL (full config)" # ~ 2 min
-tests/compat.sh -e '3DES\|DES-CBC3' -f 'NULL\|DES\|RC4\|ARCFOUR'
+OPENSSL_CMD="$OPENSSL_LEGACY" GNUTLS_CLI="$GNUTLS_LEGACY_CLI" GNUTLS_SERV="$GNUTLS_LEGACY_SERV" tests/compat.sh -e '3DES\|DES-CBC3' -f 'NULL\|DES\|RC4\|ARCFOUR'
 
 msg "test/build: curves.pl (gcc)" # ~ 4 min
 cleanup
@@ -311,7 +367,6 @@
 CC=gcc CFLAGS='-Werror -m32' make
 fi # x86_64
 
-if which arm-none-eabi-gcc >/dev/null; then
 msg "build: arm-none-eabi-gcc, make" # ~ 10s
 cleanup
 cp "$CONFIG_H" "$CONFIG_BAK"
@@ -328,9 +383,7 @@
 scripts/config.pl unset MBEDTLS_MEMORY_BACKTRACE # execinfo.h
 scripts/config.pl unset MBEDTLS_MEMORY_BUFFER_ALLOC_C # calls exit
 CC=arm-none-eabi-gcc AR=arm-none-eabi-ar LD=arm-none-eabi-ld CFLAGS=-Werror make lib
-fi # arm-gcc
 
-if which armcc >/dev/null && armcc --help >/dev/null 2>&1; then
 msg "build: armcc, make"
 cleanup
 cp "$CONFIG_H" "$CONFIG_BAK"
@@ -351,7 +404,6 @@
 scripts/config.pl unset MBEDTLS_MEMORY_BUFFER_ALLOC_C # calls exit
 scripts/config.pl unset MBEDTLS_PLATFORM_TIME_ALT # depends on MBEDTLS_HAVE_TIME
 CC=armcc AR=armar WARNING_CFLAGS= make lib
-fi # armcc
 
 if which i686-w64-mingw32-gcc >/dev/null; then
 msg "build: cross-mingw64, make" # ~ 30s