make : added target shortest

shortest only run fast part of playTests.sh .
cc @iburinoc

tests/Makefile

@@ -253,6 +253,9 @@ zstd-playTests: datagen
 	file $(ZSTD)
 	ZSTD="$(QEMU_SYS) $(ZSTD)" ./playTests.sh $(ZSTDRTTEST)
 
+shortest: ZSTDRTTEST=
+shortest: test-zstd
+
 test: test-zstd test-fullbench test-fuzzer test-zstream test-invalidDictionaries test-legacy test-decodecorpus
 ifeq ($(QEMU_SYS),)
 test: test-pool

tests/playTests.sh

@@ -316,8 +316,9 @@ $ECHO "\n**** gzip compatibility tests **** "
 GZIPMODE=1
 $ZSTD --format=gzip -V || GZIPMODE=0
 if [ $GZIPMODE -eq 1 ]; then
+    $ECHO "gzip support detected"
     GZIPEXE=1
-    which gzip || GZIPEXE=0
+    gzip -V || GZIPEXE=0
     if [ $GZIPEXE -eq 1 ]; then
         ./datagen > tmp
         $ZSTD --format=gzip -f tmp