---
title: testing.assertEmpty() function
description: testing.assertEmpty() tests if an input stream is empty. If not empty, the function returns an error.
url: https://docs.influxdata.com/flux/v0/stdlib/testing/assertempty/
estimated_tokens: 801
product: Flux
version: v0
---

# testing.assertEmpty() function

-   Flux 0.18.0+
-   View InfluxDB support

`testing.assertEmpty()` tests if an input stream is empty. If not empty, the function returns an error.

assertEmpty can be used to perform in-line tests in a query.

##### Function type signature

```js
(<-tables: stream[A]) => stream[A]
```

For more information, see [Function type signatures](/flux/v0/function-type-signatures/).

## Parameters

### tables

Input data. Default is piped-forward data (`<-`).

## Examples

### Check if there is a difference between streams

This example uses `testing.diff()` to output the difference between two streams of tables. `testing.assertEmpty()` checks to see if the difference is empty.

```js
import "sampledata"
import "testing"

want = sampledata.int()
got = sampledata.float() |> toInt()

got
    |> testing.diff(want: want)
    |> testing.assertEmpty()
```

[tests](/flux/v0/tags/tests/)