Move their common methods into an interface and have each of them
implement it.  Import them both.  Have the test code refer to the
interface and construct one or the other based on some condition.

    interface A
    {
        void foo();
    }

    class B implements A
    {
        void foo() { System.out.println( "B.foo" ); }
    }

    class C implements A
    {
        void foo() { System.out.println( "C.foo" ); }
    }

    void testA( A a ) { a.foo(); }
    void testB() { test( new B() ); }
    void testC() { test( new C() ); }