add symlink to types.ts in tests folders, so IDE won't complain

IDE was complaining about undefined types in tests.

Adding a symbolic link tests/types.ts -> src/types.ts  is  the  cleanest
solution here because it does not require changing each  test  suite  to
import the types neither redeclaring the types.

Author: uwla

tests/types.ts

@@ -0,0 +1 @@
+../src/types.ts