test: Added test checking for memory leaks.

Check for memory leaks on the C++ side by measuring memoryUsage().external, difference is measured
within reason.

package.json

@@ -30,7 +30,7 @@
     "typedoc": "typedoc --out docs --target es6 --theme minimal --mode file src",
     "lint": "tslint -c tslint.json --project .",
     "pretest": "npm run clean && npm run lint && npm run debug-build",
-    "test": "nyc mocha --ui mocha-typescript test/test_**.ts",
+    "test": "nyc mocha --expose-gc --ui mocha-typescript test/test_**.ts",
     "coverage": "nyc report --reporter=text-lcov | coveralls",
     "watch": "mocha-typescript-watch",
     "prepare": "npm run lint && tsc",

test/test_native.ts

@@ -65,4 +65,17 @@ export class TestNative {
     assert.isNotEmpty(result);
     assert.deepStrictEqual(target, result);
   }
+
+  @test
+  'memory leaks'() {
+    gc();
+    const memBefore = process.memoryUsage();
+    for (let i = 0; i < 1024; i++) {
+      const buffer = serializeNative(new ArrayBuffer(1024));
+      assert.isAbove(buffer.byteLength, 1024);
+    }
+    gc();
+    const memAfter = process.memoryUsage();
+    assert.isAtMost(memAfter.external - memBefore.external, 1024);
+  }
 }