Mocha expects without casting

hash_ext.rb

#Only include this during your tests, no need in Development or production.

class Hash
  def stringify
    inject({}){|memo,(k,v)| memo[k.to_s] = v.to_s; memo}
  end
end

prices.rb

FactoryGirl.define do
  factory :price do
    amount {rand(1..99).to_f}
    name "MyString"
    brief "MyString"
    target {Price::VALID_TARGETS.sample.to_sym}
    association :product, strategy: :build
  end
end

prices_controller_spec.rb

product.prices.any_instance.expects(:update).with(valid_attributes.stringify_keys)
put :update, {id: price.to_param, product_id: product.id, price: valid_attributes}, valid_session

result:

PricesController PUT update with valid params updates the requested price
  Failure/Error: put :update, {id: price.to_param, product_id: product.id, price: valid_attributes}, valid_session
  MiniTest::Assertion:
      unexpected invocation: #<AnyInstance:Price>.update('amount' => '46.0', 'name' => 'MyString', 'brief' => 'MyString', 'target' => 'distributor')
      unsatisfied expectations:
        - expected exactly once, not yet invoked: #<AnyInstance:Price>.update('amount' => 46.0, 'name' => 'MyString', 'brief' => 'MyString', 'target' => :distributor)

Fixed issue by stringifying everything in the valid_attributes:

product.prices.any_instance.expects(:update).with(valid_attributes.stringify)
put :update, {id: price.to_param, product_id: product.id, price: valid_attributes}, valid_session

Also see the hash_ext.rb file. I added it to my spec/support folder.