add types test

package.json

@@ -5,7 +5,7 @@
   "main": "index.js",
   "types": "index.d.ts",
   "scripts": {
-    "test": "nyc --reporter=html mocha"
+    "test": "nyc --reporter=html mocha && ts-node test/tsd.ts"
   },
   "repository": {
     "type": "git",
@@ -24,7 +24,10 @@
   },
   "homepage": "https://github.com/invertase/a2a#readme",
   "devDependencies": {
+    "@types/node": "^10.12.4",
     "mocha": "^5.2.0",
-    "nyc": "^13.0.1"
+    "nyc": "^13.0.1",
+    "ts-node": "^7.0.1",
+    "typescript": "^3.1.6"
   }
 }

test/tsd.ts

@@ -0,0 +1,11 @@
+import a2a from '../';
+
+a2a(Promise.resolve(1))
+  .then(([err, result]) => {
+    console.log(result as number);
+  });
+
+a2a([Promise.resolve(1)])
+  .then(([err, result]) => {
+    console.log(result as number[]);
+  });

tsconfig.json

@@ -0,0 +1,12 @@
+{
+  "compilerOptions": {
+    "target": "esnext",
+    "module": "commonjs",
+    "lib": ["es2015"],
+    "strict": true,
+    "moduleResolution": "node",
+    "types": ["node"],
+    "esModuleInterop": true
+  },
+  "include": ["index.d.ts", "test/*.ts"]
+}