Apex Stub API with Static Methods

CMTService.cls

public with sharing class CMTService {
	public List<CMTWrapper> getCMTs() {
		List<CMTWrapper> cmtWrappers = new List<CMTWrapper>();
		List<CMT__mdt> cmts = [SELECT Example_Field_1__c, Example_Field_2_c FROM CMT__mdt];

		for(CMT__mdt c : cmts) {
			CMTWrapper cmtWrapper = new CMTWrapper(c.Example_Field_1__c, c.Example_Field_2__c);
			cmtWrappers.add(cmtWrapper);
		}
		return cmtWrappers;
	}
                
	public class CMTWrapper {
		public String exampleField1;
		public String exampleField2;

		public CMTWrapper(String exampleField1, String exampleField2) {
			this.exampleField1 = exampleField1;
			this.exampleField2 = exampleField2;
		}
	}
}

ExampleController.cls

public with sharing class ExampleController {
	public static CMTService cmtService { get {
		if(cmtService == null {
			cmtService = new cmtService();
		}
		return cmtService;
	} set {
		cmtService = value;
	}}

	public ExampleController(ApexPage.StandardController ctrl) {
		//Usual constructor setup stuff. Setting Ids, etc.
	}

	@RemoteAction
	@AuraEnabled
	public static Map<String, Object> doStuffThatNeedsCMTs() {
		Map<String, Object> response = new Map<String, Object>();
		List<CMTService.CMTWrapper> cmts = cmtService.getCMTs();

		//Do stuff that needs CMTs

		response.put('result', resultFromWorkWithCMTs);
		return response;
	}
}

ExampleControllerTest.cls

@isTest
private class ExampleControllerTest {
	static testmethod void testDoStuff {
		List<CMTService.CMTWrapper> cmtWrappers = new List<CMTService.CMTWrapper>();
		CMTService.CMTWrapper exampleCMT1 = new CMTService.CMTWrapper(
			'Config1',
			'Config2'
		);
		cmtWrappers.add(exampleCMT1);

		CMTService.CMTWrapper exampleCMT2 = new CMTService.CMTWrapper(
			'Config3',
			'Config4'
		);
		cmtWrappers.add(exampleCMT2);

		CMTServiceMock cmtMock = new CMTServiceMock(cmtWrappers);
		CMTService mockService = (CMTService)Test.createStub(CMTService.class, cmtMock);

		ExampleController.cmtService = mockService;

		Test.startTest();

		ExampleController.doStuffThatNeedsCMTs();

		Test.stopTest();

		//Asserts goes here
	}
		
	public class CMTServiceMock implements System.StubProvider {
		public List<CMTService.CMTWrapper> cmtWrappers = new List<CMTService.CMTWrapper>();

		public CMTServiceMock(List<CMTService.CMTWrapper> cmtWrappers) {
			this.cmtWrappers = cmtWrappers;
		}

		public Object handleMethodCall(Object stubbedObject, String stubbedMethodName,
			Type returnType, List<Type> listOfParamTypes, List<String> listOfParamNames,
			List<Object> listOfArgs) {
			if(stubbedMethodName == 'getCMTs') {
				return cmtWrappers;
			} else {
				return null;
			}
		}
	}
}