[BUG] Maven plugin ignore sourceFolder for test classes

Description

I am using the maven plugin to generate the code.
The following xml snippet shows the configuration:

<configuration>
	<output>${project.basedir}</output>
	<!-- specify the swagger yaml -->
	<inputSpec>${project.basedir}/../api/swagger/swagger.yaml</inputSpec>
	<!-- target to generate java client code -->
	<language>java</language>
	<generateApiTests>true</generateApiTests>
	<generateModelTests>true</generateModelTests>
	<configOptions>
		<!-- dateLibrary>java8</dateLibrary -->
		<dateLibrary>joda</dateLibrary>
		<invokerPackage>com.someco.api.client.invoker</invokerPackage>
		<apiPackage>com.someco.api.client.api</apiPackage>
		<modelPackage>com.someco.api.client.model</modelPackage>
		<sourceFolder>src/gen/java</sourceFolder>
		<serializableModel>true</serializableModel>
		<hideGenerationTimestamp>true</hideGenerationTimestamp>
	</configOptions>
	<!-- override the default library to jersey2 -->
	<library>retrofit2</library>
</configuration>

The API and model classes are generated in the expected folder src/gen/java, but the test classes are still generated in src/test/java

openapi-generator version

Latest version

OpenAPI declaration file content or url

Any definition

Command line used for generation

I have used the maven plugin

Steps to reproduce

Run mvn clean install

Start with the Maven plugin configuration handling for sourceFolder and compare where API/model tests versus generated source files are written. Reproduce the issue with the provided configuration using mvn clean install. Done means test classes also use src/gen/java rather than remaining in src/test/java.