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# CustomTestArgumentEncodable

A protocol for customizing how arguments passed to parameterized tests are
encoded, which is used to match against when running specific arguments.

```
protocol CustomTestArgumentEncodable : Sendable
```

## Overview

The testing library checks whether a test argument conforms to this
protocol, or any of several other known protocols, when running selected
test cases. When a test argument conforms to this protocol, that conformance
takes highest priority, and the testing library will then call
[`encodeTestArgument(to:)`](/documentation/Testing/CustomTestArgumentEncodable/encodeTestArgument(to:)) on the argument. A type that conforms to this
protocol is not required to conform to either `Encodable` or `Decodable`.

See [Implementing parameterized tests](/documentation/Testing/ParameterizedTesting) for a list of the other supported ways to
allow running selected test cases.

## See Also

[Implementing parameterized tests](/documentation/Testing/ParameterizedTesting)

Specify different input parameters to generate multiple test cases from a test function.


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