How to test a http calls from a second class func call from within first class (APEX class testing/salesforce testing)

I have an apex class A. I'm calling the function of B class from within A.

class A{

B bobj=new B(); B.function2();

function1(); //within class A

}

This function1 and function2 are http calls to 2 diff rest services.

I wrote a test class with httpcallmockouts for the both function1 and function2. So the order goes like this inside APex Test class-

B objB=new B();

HttpResponse res = CalloutB.getInfoFromExternalService();

A objA=new A(); HttpResponse res = CalloutA.getInfoFromExternalService();

//Till this point my test runs successfully for http calls mock

Test.startTest();

objA.function1();

//Here I get an error http callout not supported for test methods for function2 of B class.

//If I change the order above to

//A objA=new A();

//HttpResponse res = CalloutA.getInfoFromExternalService();

//B objB=new B();

//HttpResponse res = CalloutB.getInfoFromExternalService();

//Then I get error http callout not supported for test methods for function1 of A class.

Test.stopTest();

So, how do you test the http call from within another's class function calls in the first class.