in src/main/java/org/apache/sling/testing/resourceresolver/MockResourceResolver.java [456:468]
public String getParentResourceType(String resourceType) {
// normalize resource type to a path string
final String rtPath = (resourceType == null ? null : ResourceUtil.resourceTypeToPath(resourceType));
// get the resource type resource and check its super type
String resourceSuperType = null;
if (rtPath != null) {
final Resource rtResource = getResource(rtPath);
if (rtResource != null) {
resourceSuperType = rtResource.getResourceSuperType();
}
}
return resourceSuperType;
}