excerpt: "Asserts that a value is the boolean value true."
layout: manual
---
Asserts that a value is the boolean value true.
```kcl
assertIs(
@actual: bool,
error?: string,
)
```
### Arguments
| Name | Type | Description | Required |
|----------|------|-------------|----------|
| `actual` | [`bool`](/docs/kcl-std/types/std-types-bool) | Value to check. If this is the boolean value true, assert passes. Otherwise it fails.. | Yes |
| `error` | [`string`](/docs/kcl-std/types/std-types-string) | If the value was false, the program will terminate with this error message | No |
