Support Request - Implement PhpUnit test for a create mutation with Upload file fields

Hello all,

I'd like to ask your help with a PhpUnit test I'm writing for a create mutation that has an Upload! field argument.

Here is the mutation definition:
```
/**
* A mutation responsible for creating an employer node.
*
* @GraphQLMutation(
* id = "create_employer",
* secure = true,
* name = "createEmployer",
* type = "EntityCrudOutput",
* arguments = {
* "input" = "CreateEmployerInput"
* }
* )
*/
```

Where CreateEmployerInput is:
```
/**
* @GraphQLInputType(
* id = "create_employer_input",
* name = "CreateEmployerInput",
* fields = {
* "title" = "String!",
* "field_advertiser_name" = "String!",
* "field_logo" = "FileUploadInput",
* }
* )
*/
```

In my PHP unit test I'm using this:
```
// Execute mutation and assert result.
$this->assertResults($this->getQueryFromFile('mutations/create_employer_mutation.gql'), [], [
'creteEmployer' => [
'errors' => [],
'violations' => [],
'entity' => [
'entityLabel' => 'Employer test',
],
],
], $metadata);
```

And the mutation graphql looks like this:

```
mutation {
createEmployer(input:{
title: "Employer test",
field_advertiser_name:"Employer test adv name",
field_logo:"..",
}) {
violations {
path
message
}
errors
entity {
entityLabel
}
}
}
```

Does anyone know how can I test the `field_logo`?