Implement Synth as an exchange rate provider (#574)

* Implement Synth as an exchange rate provider

* Add assertions to provider interface test

* Assert the correct provider error is raised

* Remove unnecessary parens

test/interfaces/exchange_rate_provider_interface_test.rb

@@ -0,0 +1,27 @@
+require "test_helper"
+
+module ExchangeRateProviderInterfaceTest
+  extend ActiveSupport::Testing::Declarative
+
+  test "exchange rate provider interface" do
+    assert_respond_to @subject, :fetch_exchange_rate
+  end
+
+  test "exchange rate provider response contract" do
+    accounting_for_http_calls do
+      response = @subject.fetch_exchange_rate from: "USD", to: "MXN", date: Date.current
+
+      assert_respond_to response, :rate
+      assert_respond_to response, :success?
+      assert_respond_to response, :error
+      assert_respond_to response, :raw_response
+    end
+  end
+
+  private
+    def accounting_for_http_calls
+      VCR.use_cassette "synth_exchange_rate" do
+        yield
+      end
+    end
+end

test/models/exchange_rate_test.rb

@@ -1,7 +1,42 @@
 require "test_helper"
 
 class ExchangeRateTest < ActiveSupport::TestCase
-  # test "the truth" do
-  #   assert true
-  # end
+  test "find rate in db" do
+    assert_equal exchange_rates(:day_29_ago_eur_to_usd),
+      ExchangeRate.find_rate_or_fetch(from: "EUR", to: "USD", date: 29.days.ago.to_date)
+  end
+
+  test "fetch rate from provider when it's not found in db" do
+    ExchangeRate
+      .expects(:fetch_rate_from_provider)
+      .returns(ExchangeRate.new(base_currency: "USD", converted_currency: "MXN", rate: 1.0, date: Date.current))
+
+    ExchangeRate.find_rate_or_fetch from: "USD", to: "MXN", date: Date.current
+  end
+
+  test "provided rates are saved to the db" do
+    VCR.use_cassette "synth_exchange_rate" do
+      assert_difference "ExchangeRate.count", 1 do
+        ExchangeRate.find_rate_or_fetch from: "USD", to: "MXN", date: Date.current
+      end
+    end
+  end
+
+  test "retrying, then raising on provider error" do
+    Faraday.expects(:get).returns(OpenStruct.new(success?: false)).times(3)
+
+    error = assert_raises Provider::Base::ProviderError do
+      ExchangeRate.find_rate_or_fetch from: "USD", to: "MXN", date: Date.current
+    end
+
+    assert_match "Failed to fetch exchange rate from Provider::Synth", error.message
+  end
+
+  test "retrying, then raising on network error" do
+    Faraday.expects(:get).raises(Faraday::TimeoutError).times(3)
+
+    assert_raises Faraday::TimeoutError do
+      ExchangeRate.find_rate_or_fetch from: "USD", to: "MXN", date: Date.current
+    end
+  end
 end

test/models/provider/synth_test.rb

@@ -0,0 +1,9 @@
+require "test_helper"
+
+class Provider::SynthTest < ActiveSupport::TestCase
+  include ExchangeRateProviderInterfaceTest
+
+  setup do
+    @subject = Provider::Synth.new
+  end
+end

test/test_helper.rb

@@ -1,6 +1,17 @@
 ENV["RAILS_ENV"] ||= "test"
 require_relative "../config/environment"
 require "rails/test_help"
+require "minitest/mock"
+require "minitest/autorun"
+require "mocha/minitest"
+
+VCR.configure do |config|
+  config.cassette_library_dir = "test/vcr_cassettes"
+  config.hook_into :webmock
+  config.ignore_localhost = true
+  config.default_cassette_options = { erb: true }
+  config.filter_sensitive_data("<SYNTH_API_KEY>") { ENV["SYNTH_API_KEY"] }
+end
 
 module ActiveSupport
   class TestCase
@@ -16,3 +27,5 @@ module ActiveSupport
     end
   end
 end
+
+Dir[Rails.root.join("test", "interfaces", "**", "*.rb")].each { |f| require f }

test/vcr_cassettes/synth_exchange_rate.yml

@@ -0,0 +1,69 @@
+---
+http_interactions:
+- request:
+    method: get
+    uri: https://api.synthfinance.com/rates/historical?date=<%= Date.current.to_s %>&from=USD&to=MXN
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      User-Agent:
+      - Faraday v2.9.0
+      Authorization:
+      - Bearer <SYNTH_API_KEY>
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Date:
+      - Wed, 27 Mar 2024 02:54:11 GMT
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '138'
+      Connection:
+      - keep-alive
+      Cf-Ray:
+      - 86ac182ad9ec7ce5-LAX
+      Cf-Cache-Status:
+      - DYNAMIC
+      Cache-Control:
+      - max-age=0, private, must-revalidate
+      Etag:
+      - W/"46780d3f34043bb3bc799b1efae62418"
+      Strict-Transport-Security:
+      - max-age=63072000; includeSubDomains
+      Vary:
+      - Accept-Encoding
+      Referrer-Policy:
+      - strict-origin-when-cross-origin
+      Rndr-Id:
+      - 3ca97b82-f963-43a3
+      X-Content-Type-Options:
+      - nosniff
+      X-Frame-Options:
+      - SAMEORIGIN
+      X-Permitted-Cross-Domain-Policies:
+      - none
+      X-Render-Origin-Server:
+      - Render
+      X-Request-Id:
+      - 64731a8c-4cad-4e42-81c9-60b0d3634a0f
+      X-Runtime:
+      - '0.021432'
+      X-Xss-Protection:
+      - '0'
+      Server:
+      - cloudflare
+      Alt-Svc:
+      - h3=":443"; ma=86400
+    body:
+      encoding: ASCII-8BIT
+      string: '{"data":{"date":"<%= Date.current.to_s %>","source":"USD","rates":{"MXN":16.64663}},"meta":{"total_records":1,"credits_used":1,"credits_remaining":976}}'
+  recorded_at: Wed, 27 Mar 2024 02:54:11 GMT
+recorded_with: VCR 6.2.0