Create tests for CoinGecko api.

apps/explorer/lib/explorer/exchange_rates/source/coin_gecko.ex

@@ -9,7 +9,6 @@ defmodule Explorer.ExchangeRates.Source.CoinGecko do
   import Source, only: [decode_json: 1, to_decimal: 1, headers: 0]
 
   @behaviour Source
-  @headers
 
   @impl Source
   def fetch_exchange_rates do

apps/explorer/test/explorer/exchange_rates/source/coin_gecko_test.exs

@@ -0,0 +1,97 @@
+defmodule Explorer.ExchangeRates.Source.CoinGeckoTest do
+  use ExUnit.Case
+
+  alias Explorer.ExchangeRates.Token
+  alias Explorer.ExchangeRates.Source.CoinGecko
+  alias Plug.Conn
+
+  @json_btc_price """
+  {
+    "rates": {
+      "usd": {
+        "name": "US Dollar",
+        "unit": "$",
+        "value": 6547.418,
+        "type": "fiat"
+      }
+    }
+  }
+  """
+
+  @json_mkt_data """
+  [
+    {
+      "id": "poa-network",
+      "symbol": "poa",
+      "name": "POA Network",
+      "image": "https://assets.coingecko.com/coins/images/3157/large/poa.jpg?1520829019",
+      "current_price": 0.114782883773693,
+      "market_cap": 25248999.6735956,
+      "market_cap_rank": 185,
+      "total_volume": 2344442.13578437,
+      "high_24h": 0.115215129840519,
+      "low_24h": 0.101039753612939,
+      "price_change_24h": 0.0135970966607094,
+      "price_change_percentage_24h": 13.437753511298,
+      "market_cap_change_24h": 3058195.58191147,
+      "market_cap_change_percentage_24h": 13.7813644304017,
+      "circulating_supply": "219935174.0",
+      "total_supply": 252193195,
+      "ath": 0.935923393359191,
+      "ath_change_percentage": -87.731057963078,
+      "ath_date": "2018-05-10T09:45:31.809Z",
+      "roi": null,
+      "last_updated": "2018-10-23T01:25:31.764Z"
+    }
+  ]
+  """
+
+  describe "fetch_exchange_rates" do
+    setup do
+      bypass = Bypass.open()
+      Application.put_env(:explorer, CoinGecko, base_url: "http://localhost:#{bypass.port}")
+
+      {:ok, bypass: bypass}
+    end
+
+    test "with successful request", %{bypass: bypass} do
+      Bypass.expect(bypass, "GET", "/exchange_rates", fn conn ->
+        Conn.resp(conn, 200, @json_btc_price)
+      end)
+
+      Bypass.expect(
+        bypass,
+        fn conn -> Conn.resp(conn, 200, @json_mkt_data) end
+      )
+
+      {:ok, expected_date, 0} = "2018-10-23T01:25:31.764Z" |> DateTime.from_iso8601()
+
+      expected = [
+        %Token{
+          available_supply: Decimal.new("252193195"),
+          btc_value: Decimal.new("0.00001753101509231471092879666458"),
+          id: "poa-network",
+          last_updated: expected_date,
+          market_cap_usd: Decimal.new("25248999.6735956"),
+          name: "POA Network",
+          symbol: "poa",
+          usd_value: Decimal.new("0.114782883773693"),
+          volume_24h_usd: Decimal.new("2344442.13578437")
+        }
+      ]
+
+      assert {:ok, ^expected} = CoinGecko.fetch_exchange_rates()
+    end
+
+    test "with bad request response", %{bypass: bypass} do
+      error_text = ~S({"error": "bad request"})
+
+      Bypass.expect(
+        bypass,
+        fn conn -> Conn.resp(conn, 400, error_text) end
+      )
+
+      assert {:error, "bad request"} == CoinGecko.fetch_exchange_rates()
+    end
+  end
+end