---
title: testing.shouldError() function
description: >
  `testing.shouldError()` calls a function that catches any error and checks that the error matches the expected value.
menu:
  flux_v0_ref:
    name: testing.shouldError
    parent: testing
    identifier: testing/shouldError
weight: 101
flux/v0/tags: [tests]
introduced: 0.174.0
---

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`testing.shouldError()` calls a function that catches any error and checks that the error matches the expected value.



##### Function type signature

```js
(fn: () => A, want: regexp) => stream[{v: string}]
```

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

## Parameters

### fn
({{< req >}})
Function to call.



### want
({{< req >}})
Regular expression to match the expected error.




## Examples

### Test die function errors

```js
import "testing"

testing.shouldError(fn: () => die(msg: "error message"), want: /error message/)

```