# TEST MOCHA, got error "a.filter is not a function"

**URL:** <https://discourse.nodered.org/t/test-mocha-got-error-a-filter-is-not-a-function/60612>\
**Category:** General\
**Tags:** function-node\
**Created:** [31 March 2022 19:15 UTC](https://discourse.nodered.org/t/test-mocha-got-error-a-filter-is-not-a-function/60612 "2022-03-31T19:15:47Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![rita7](https://avatars.discourse-cdn.com/v4/letter/r/9de053/32.png) [@rita7](https://discourse.nodered.org/u/rita7)\
**Post date:** [31 March 2022 19:15 UTC](https://discourse.nodered.org/t/test-mocha-got-error-a-filter-is-not-a-function/60612/1 "2022-03-31T19:15:47Z")

</div>

I try use MOCHA test. Need remove dublicate words in array. It my test. I got errors "TypeError: a.filter is not a function  
at removeDuplicateWords (test.js:3:14)  
at Context. (test.js:16:24)  
at processImmediate (internal/timers.js:461:21)"  
my test:

```auto
function removeDuplicateWords(a=[]){ 
	let arr2= a.filter((item, index)=>a.indexOf(item) == index )
return arr2	
}

```

////

```auto
const assert = require("chai").assert;

describe("Basic tests", () => {
  it("Testing for fixed tests", () => {
    assert.strictEqual(removeDuplicateWords('alpha beta beta gamma gamma gamma delta alpha beta beta gamma gamma gamma delta'), 'alpha beta gamma delta');
  });
});

```

---

<div class="post-metadata">

**Author:** ![Steve-Mcl](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/steve-mcl/32/4826_2.png) [@Steve-Mcl](https://discourse.nodered.org/u/Steve-Mcl)\
**Post date:** [31 March 2022 22:07 UTC](https://discourse.nodered.org/t/test-mocha-got-error-a-filter-is-not-a-function/60612/2 "2022-03-31T22:07:44Z")

</div>

You are sending a string into the function, not an array. String doesn't have a .filter function.

> [@rita7](#):
>
> `assert.strictEqual(removeDuplicateWords('alpha beta beta gamma gamma gamma delta alpha beta beta gamma gamma gamma delta'), 'alpha beta gamma delta');`

Try

`assert.strictEqual(removeDuplicateWords('alpha beta beta gamma gamma gamma delta alpha beta beta gamma gamma gamma delta'.split(' ')), 'alpha beta gamma delta');`

---

<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [30 May 2022 22:08 UTC](https://discourse.nodered.org/t/test-mocha-got-error-a-filter-is-not-a-function/60612/3 "2022-05-30T22:08:08Z")

</div>

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