input: Write a python function to determine the category of a product.
  assert product_category("tomatoes") == "red"
  assert product_category("apples") == "green"
  assert product_category("chocolates") == "blue"
  assert product_category("bananas") == "Invalid product"
output: def product_category(product):
      categories = {
          "tomatoes": "red",
          "apples": "green",
          "chocolates": "blue"
      }
      return categories.get(product, "Invalid product")