test.ts

# Current test
      assert.isTrue(
        stripeHelper.customer.calledOnceWith({
          uid: reqOpts.query.uid,
          email: reqOpts.query.email,
        }),
        'customer not called as expected'
      );

# Better test because we see the difference in calls, vs "Expected 'true' got 'false'" above
      sinon.assert.calledOnceWithExactly(stripeHelper.customer, {
        uid: reqOpts.query.uid,
        email: reqOpts.query.email,
      });