# Our First Test

Writing [self-testing
code](http://www.martinfowler.com/bliki/SelfTestingCode.html) is a
powerful tool for building robust and maintainable software. While there
are many ways of writing test code, I enjoy using [Test Driven
Development](#) for solving problems like this.

Following the ideas of TDD, we'll write the simplest test we can that
results in failure. We expect `deleteNth([], 0)` to return an empty
array. After writing this test and running our test suite, the test
fails:

    deleteNth is not defined

We need to export `deleteNth` from our module under test and import it
into our test file. After making those changes, the test suite is still
failing:

    expected undefined to deeply equal []

Because our `deleteNth` method isn't returning anything our assertion
that it should return `[]` is failing. A quick way to bring our test
suite into a passing state is to have `deleteNth` return `[]`.

index.js

@@ -1,3 +1,3 @@
-function deleteNth(arr,x){
-    // ...
+export function deleteNth(arr,x){
+    return [];
 }

test/index.js

@@ -1,7 +1,10 @@
+import { deleteNth } from "../";
 import { expect } from "chai";
 
-describe("index", function() {
+describe("deleteNth", function() {
 
-  it("works");
+    it("deletes occurrences of an element if it occurs more than n times", function () {
+        expect(deleteNth([], 0)).to.deep.equal([]);
+    });
 
 });