Testing promises yields expected [Function] to throw

I am having an issue with a expected [Function] to throw Error message in my tests. Looking this up the suggestion is to add a catch block to my promises but I do not want to add catch blocks everywhere just so I can keep throwing the same exception. My catch will be in the final code (illustrated in my working test at bottom). Code works fine but fails to pass the desired commented out test about thrown errors.

I am not sure where the issue is - is it something I am missing in my promise or is it related to expect?

My code:

// Common wrapper calling function used by other methods
MyClass.prototype.doCall = function(func) {

  // Create a promise
  var p = new P(function(resolve, reject) {

  // Call async function - might return an error message - we want to throw an error for thay
    mws.client.invoke(func, function(r) {
      if (data.ErrorResponse) {
       // Throwing error here doesn't seem to make it cascade at all - just reject message
        return reject(data.ErrorResponse.Error.Message);
      }
      resolve(data);
    });
  }).
  catch(function(e) {
    // Have to throw here
    throw new Error(e);
  });
  return p.delay(timeout);
};

// Here's the method I call in my tests
MyClass.prototype.fetchOrders = function(from, to) {
  var self = this;
  return this.doCall(o)
    .then(function(orders) {
    // Probably not related to issue but here just in case
      return P.map(orders, function(r) {
        return self.fetchOrderById(r.OrderId);
      });
    });
};

My test:

// This works fine - I can catch the error in my final code which is what I want
order.fetchOrders()
  .then(function(orders) {
    expect(orders).to.have.length(1);
    done();
  }).catch(function(e) {
    console.log(e);
    done();
  })

// On the other hand this fails with: expected [Function] to throw Error
expect(order.fetchOrderList.bind(order, from, to)).to.throw(Error);