Function
onChild
Common
```kotlin
@CheckResult
fun SemanticsNodeInteraction.onChild(): SemanticsNodeInteraction
```
Returns exactly one child of this node.
Use this only if this node has exactly one child.
Any subsequent operation on its result will expect exactly one element found (unless
`SemanticsNodeInteraction.assertDoesNotExist` is used) and will throw `AssertionError` if none or
more than one element is found.