[node] homogenize zlib input to Buffer or string and results to Buffer

types/node/node-tests.ts

@@ -2820,3 +2820,19 @@ namespace async_hooks_tests {
     const tId: number = async_hooks.triggerAsyncId();
     const eId: number = async_hooks.executionAsyncId();
 }
+
+////////////////////////////////////////////////////
+/// zlib tests : http://nodejs.org/api/zlib.html ///
+////////////////////////////////////////////////////
+
+namespace zlib_tests {
+    {
+        const gzipped = zlib.gzipSync('test');
+        const unzipped = zlib.gunzipSync(gzipped.toString());
+    }
+
+    {
+        const deflate = zlib.deflateSync('test');
+        const inflate = zlib.inflateSync(deflate.toString());
+    }
+}