Rails database persistance through tests

I'm writing tests for my current rails project and I'm running into an issue whereby changes made to the test database through a post call aren't persisting long enough to test the changes.

Basically, I have objects which have a barcode assigned to them. I have put in a form whereby a user can scan in several barcodes to change multiple objects at a time. This is the code.

objecta_controller.rb:

  def change_many
    @barcodes = params[:barcodes].split()
    @objects = ObjectA.order("barcode").where(barcode: @barcodes)
    @objects.each do |b|
      if can? :change, b
        b.state_b()
      end
    end
  end

(Note: @barcodes is a string of barcodes seperated by whitespace)

objecta_controller_test.rb:

test "change object" do
    sign_in_as(:admin_staff)

    b = ObjectA.new(
      barcode: "PL123456",
      current_status: "state_a")
    post :change_many, { barcodes: b.barcode }

    assert_equal("state_b", b.current_status, "Current status incorrect: #{b.to_s}")
  end

Using byebug, I've ascertained that the objects do change state in the change_many method, but once it gets back to the test the object's state reverts back to its old one and the test fails.