How to properly mock objects in RSpec? - ruby

Question

I have a simple class, which generates a download URL to a file stored on S3 and I need to write a unit test to test this class. So far I've had no luck.
class S3DownloadUrlGenerator
def initialize(filename)
#filename = filename
end
def presigned_url
signer = Aws::S3::Presigner.new(client: s3)
signer.presigned_url(
:get_object,
bucket: "my-bucket",
key: filename,
response_content_disposition: "attachment",
)
end
private
def s3
#s3 ||= Aws::S3::Client.new(
region: "my-region,
http_open_timeout: 5,
http_read_timeout: 25,
)
end
attr_reader :filename
end
I want to test if calling #presigned_url on an instance of S3DownloadUrlGenerator returns a URL.
This is my test:
describe S3DownloadUrlGenerator do
before do
allow(Aws::S3::Client).to receive(:new) { s3_client }
end
let(:s3_client) { spy("s3 client") }
let(:presigner) { spy("s3 presigner") }
it "generates download URL for a file" do
expect(Aws::S3::Presigner).to receive(:new).with(client: s3_client).and_return(presigner)
expect(presigner).to receive(:presigned_url).with(
:get_object,
bucket: "my-test-bucket",
key: "test_file.txt",
response_content_disposition: "attachment",
).and_return("https://www.example.com")
expect(described_class.new("Test_file.txt").presigned_url).to eq("https://www.example.com")
end
end
but I get an error:
Failure/Error: expect(described_class.new("Test_file.txt").presigned_url).to eq("https://www.example.com")
expected: "https://www.example.com"
got: #<Double "s3 presigner">
(compared using ==)
I am bit new to this and I would like to learn how to properly test such cases. Thank you very much for the help.

Answer 1

bucket and key parameters differ in actual calling and mocking.
Use below code it works:
describe S3DownloadUrlGenerator do
before do
allow(Aws::S3::Client).to receive(:new) { s3_client }
end
let(:s3_client) { spy("s3 client") }
let(:presigner) { spy("s3 presigner") }
it "generates download URL for a file" do
expect(Aws::S3::Presigner).to receive(:new).with(client: s3_client).and_return(presigner)
expect(presigner).to receive(:presigned_url).with(
:get_object,
bucket: "my-bucket",
key: "Test_file.txt",
response_content_disposition: "attachment",
).and_return("https://www.example.com")
expect(described_class.new("Test_file.txt").presigned_url).to eq("https://www.example.com")
end
end