How to test if a store (mst) has a variable set during a call

Question

Say I wish to test if the "loading" property is set during the execution of tests:

export const MyModel = types
  .model("MyModel", {
    frontendId: types.optional(types.identifier, () => v4()), // id only for frontend
    id: types.maybeNull(types.identifier, () => v4()),
    loading: types.optional(types.boolean, false),
  })
  .actions((self) => ({
    load: flow(function* load(env) {
      self.loading = true;
      yield env.jsonFetch("someurl")
      self.loading = false;
    }),    
  }))

test("Load data from", async () => {
  const model = MyModel.create({}, {
    jsonFetch: () => {
      console.log('fetch called');
    }
  });

  await model.load(); // How would I test during this call that the store has set something correctly?
}