why are brackets used in this assert_equal statement

Question

In the book Agile Web Development with Rails, they're teaching how to write test unit cases:

test "product price must be positive" do
  product = Product.new(title: "By Book Title",
                        description: "yyy",
                        image_url: "zzz.jpg")
  product.price = -1
  assert product.invalid?
  assert_equal ["must be greater than or equal to 0.01"], product.errors[:price]
end

Concerning the assert_equal statement, why are brackets needed around the "must be greater than..." string. I'm assuming variable types are coming into play here, but need some clarification on why.

Thanks.

Answer 1

model.errors[:field] always returns an array of strings, even if there's only a single error.

If the assert was done without the [ ] it would always be false because it would be comparing a string to an array.

assert_equal "must be greater than or equal to 0.01", ["must be greater than or equal to 0.01"]    
=> false

assert_equal ["must be greater than or equal to 0.01"], ["must be greater than or equal to 0.01"]   
=> true