Node.js sinon stubbing a function in parallel executions causes failed tests

I have 2 test cases which test the same function just taking 2 different executions paths, so to illustrate:

MyClass.prototype.functionBeingTested = function() {
    if (this.check1()) {
        this.isCheck1Called = true;
    } else if (this.check2()) {
        this.isCheck1Called = false;
    } else {
        ...
    }
};

My 2 test cases are as follow:

it('should take check1() execution path', function() {
    var myClass= new MyClass({}, {}, {});
    var check1Stub sinon.stub(MyClass.prototype, 'check1');
    check1Stub.returns(true);
    myClass.functionBeingTested();
    myClass.isCheck1Called.should.equal(true);
});

it('should take check2() execution path', function() {
    var myClass= new MyClass({}, {}, {});
    var check2Stub sinon.stub(MyClass.prototype, 'check2');
    check2Stub.returns(true);
    myClass.functionBeingTested();
    myClass.isCheck1Called.should.equal(false);
});

Now by default, check1() returns false so I don't stub it in the second test case, but by the time the second case is running, the check1() function stub is still active and causes the second case to enter the execution path of the first case as-well, making the second case test fail.

I understand it's a problem of test running in parallel and the first sinon stub still being used by the first test case, is there anyway I can solve this problem?