Crystal Spectator - using `inject_mock`

return_mocked_object.cr

# spec.cr
require "spectator"
require "./spec_helper"

Spectator.describe OrderCalculator do
  inject_mock Database
  def_mock(Product)

  it "multiplies the product price by given quantity" do
    product = new_mock(Product)
    allow(Database).to receive(:product).and_return product
    allow(product).to receive(:price).and_return 5.0

    expect(subject.total_price(quantity: 2)).to eq 10
  end
end

# code.cr
class OrderCalculator
  def total_price(quantity : Int) : Float
    Database.product.price * quantity
  end
end

class Product
  def price : Float
    10.0
  end
end

class Database
  def self.product : Product
    Product.new
  end
end

return_primitive.cr

# spec.cr
require "spectator"
require "./spec_helper"

Spectator.describe OrderCalculator do
  inject_mock Database

  it "multiplies the product price by given quantity" do
    allow(Database).to receive(:product_price).and_return 5.0

    expect(subject.total_price(quantity: 2)).to eq 10
  end
end

# code.cr
class OrderCalculator
  def total_price(quantity : Int) : Float
    Database.product_price * quantity
  end
end

class Database
  def self.product_price : Float
    0.0
  end
end