adding test for long mode trigger

tests/playTests.sh

@@ -1276,6 +1276,14 @@ datagen > tmp_dict
 zstd --patch-from=tmp_dict -r tmp_dir && die
 rm -rf tmp*
 
+println "\n===> patch-from long mode trigger larger file test"
+
+datagen -g5000000 > tmp_dict
+datagen -g5000000 > tmp_patch
+zstd -15 --patch-from=tmp_dict tmp_patch &> tmp_out
+grep "long mode automaticaly triggered" tmp_out
+rm -rf tmp*
+
 println "\n===>   large files tests "
 
 roundTripTest -g270000000 1