Change `Market.fetch_exchange_rate/1` and supporting code to be testable

Replace default test configuration for `ExchangeRates` to use a no-op
Source and bypass :ets. This allows higher level feature tests to
run without having to manage GenServer processes when they don’t need
Exchange rate information but allows the lower tests to exercise the
specific behavior as before. Add `Token.null`.


Co-authored-by: jimmay5469 <jimmay5469@gmail.com>

apps/explorer/lib/explorer/exchange_rates/exchange_rates.ex

@@ -33,7 +33,7 @@ defmodule Explorer.ExchangeRates do
         {symbol, token}
       end
 
-    :ets.insert(table_name(), records)
+    if store() == :ets, do: :ets.insert(table_name(), records)
 
     {:noreply, state}
   end
@@ -67,7 +67,7 @@ defmodule Explorer.ExchangeRates do
       write_concurrency: true
     ]
 
-    :ets.new(table_name(), table_opts)
+    if store() == :ets, do: :ets.new(table_name(), table_opts)
 
     {:ok, %{}}
   end
@@ -83,10 +83,7 @@ defmodule Explorer.ExchangeRates do
   """
   @spec list :: [Token.t()]
   def list do
-    table_name()
-    |> :ets.tab2list()
-    |> Enum.map(fn {_, rate} -> rate end)
-    |> Enum.sort_by(fn %Token{symbol: symbol} -> symbol end)
+    list_from_store(store())
   end
 
   ## Undocumented public functions
@@ -113,4 +110,17 @@ defmodule Explorer.ExchangeRates do
       exchange_rates_source().fetch_exchange_rates()
     end)
   end
+
+  defp list_from_store(:ets) do
+    table_name()
+    |> :ets.tab2list()
+    |> Enum.map(fn {_, rate} -> rate end)
+    |> Enum.sort_by(fn %Token{symbol: symbol} -> symbol end)
+  end
+
+  defp list_from_store(_), do: []
+
+  defp store do
+    config(:store) || :ets
+  end
 end

apps/explorer/lib/explorer/exchange_rates/token.ex

@@ -29,4 +29,6 @@ defmodule Explorer.ExchangeRates.Token do
         }
 
   defstruct ~w(available_supply btc_value id last_updated market_cap_usd name symbol usd_value volume_24h_usd)a
+
+  def null, do: %__MODULE__{}
 end

apps/explorer/lib/explorer/market/market.ex

@@ -5,10 +5,9 @@ defmodule Explorer.Market do
 
   import Ecto.Query
 
-  alias Explorer.ExchangeRates
+  alias Explorer.{ExchangeRates, Repo}
   alias Explorer.ExchangeRates.Token
   alias Explorer.Market.MarketHistory
-  alias Explorer.Repo
 
   @doc """
   Get most recent exchange rate for the given symbol.
@@ -16,7 +15,7 @@ defmodule Explorer.Market do
   @spec fetch_exchange_rate(String.t()) :: Token.t()
   def fetch_exchange_rate(symbol) do
     ExchangeRates.list()
-    |> Enum.find(fn(token) -> token.symbol == symbol end)
+    |> Enum.find(fn token -> token.symbol == symbol end)
   end
 
   @doc """

apps/explorer/test/explorer/exchange_rates/exchange_rates_test.exs

@@ -11,6 +11,16 @@ defmodule Explorer.ExchangeRatesTest do
 
   setup :verify_on_exit!
 
+  setup do
+    # Use TestSource mock and ets table for this test set
+    configuration = Application.get_env(:explorer, Explorer.ExchangeRates)
+    Application.put_env(:explorer, Explorer.ExchangeRates, source: TestSource)
+
+    on_exit(fn ->
+      Application.put_env(:explorer, Explorer.ExchangeRates, configuration)
+    end)
+  end
+
   test "start_link" do
     stub(TestSource, :fetch_exchange_rates, fn -> {:ok, [%Token{}]} end)
     set_mox_global()

apps/explorer/test/explorer/market/market_test.exs

@@ -9,6 +9,8 @@ defmodule Explorer.MarketTest do
 
   describe "fetch_exchange_rate/1" do
     setup do
+      use_ets_store()
+
       {:ok, _} = ExchangeRates.start_link([])
       rate = %Token{id: "POA", symbol: "POA"}
       :ets.insert(ExchangeRates.table_name(), {rate.id, rate})
@@ -103,4 +105,19 @@ defmodule Explorer.MarketTest do
       assert fetched_record.opening_price == new_record.opening_price
     end
   end
+
+  defp use_ets_store do
+    # Use ets tables as ExchangeRates store and put some test data in to
+    # exercise Context filtering
+    exchange_config = Application.get_env(:explorer, Explorer.ExchangeRates)
+    Application.put_env(
+      :explorer,
+      Explorer.ExchangeRates,
+      Keyword.put(exchange_config, :store, :ets)
+    )
+
+    on_exit(fn ->
+      Application.put_env(:explorer, Explorer.ExchangeRates, exchange_config)
+    end)
+  end
 end

apps/explorer/test/support/fakes/no_op_source.ex

@@ -0,0 +1,10 @@
+defmodule Explorer.ExchangeRates.Source.NoOpSource do
+  @moduledoc false
+
+  alias Explorer.ExchangeRates.Source
+
+  @behaviour Source
+
+  @impl Source
+  def fetch_exchange_rates, do: {:ok, []}
+end

apps/explorer_web/lib/explorer_web/controllers/chain_controller.ex

@@ -2,6 +2,7 @@ defmodule ExplorerWeb.ChainController do
   use ExplorerWeb, :controller
 
   alias Explorer.Chain.{Address, Block, Statistics, Transaction}
+  alias Explorer.ExchangeRates.Token
   alias Explorer.Market
   alias ExplorerWeb.Chain
 
@@ -11,7 +12,7 @@ defmodule ExplorerWeb.ChainController do
       "show.html",
       chain: Statistics.fetch(),
       market_history_data: Market.fetch_recent_history(30),
-      exchange_rate: Market.fetch_exchange_rate(Application.get_env(:explorer, :coin))
+      exchange_rate: Market.fetch_exchange_rate(coin()) || Token.null()
     )
   end
 
@@ -28,6 +29,10 @@ defmodule ExplorerWeb.ChainController do
     end
   end
 
+  defp coin do
+    Application.get_env(:explorer, :coin)
+  end
+
   defp redirect_search_results(conn, %Address{} = item) do
     redirect(conn, to: address_path(conn, :show, Gettext.get_locale(), item.hash))
   end

apps/explorer_web/lib/explorer_web/views/chain_view.ex

@@ -3,11 +3,11 @@ defmodule ExplorerWeb.ChainView do
 
   def encode_market_history_data(market_history_data) do
     market_history_data
-    |> Enum.map(fn(day) -> Map.take(day, [:closing_price, :date]) end)
+    |> Enum.map(fn day -> Map.take(day, [:closing_price, :date]) end)
     |> Jason.encode()
     |> case do
-         {:ok, data} -> data
-         _ -> []
-       end
+      {:ok, data} -> data
+      _ -> []
+    end
   end
 end

apps/explorer_web/test/explorer_web/controllers/chain_controller_test.exs

@@ -60,13 +60,13 @@ defmodule ExplorerWeb.ChainControllerTest do
     end
 
     test "returns market history data", %{conn: conn} do
-      today = Date.utc_today
-      for day <- -14..0, do: insert(:market_history, date: Date.add(today, day))
+      today = Date.utc_today()
+      for day <- -40..0, do: insert(:market_history, date: Date.add(today, day))
 
       conn = get(conn, "/en")
 
       assert Map.has_key?(conn.assigns, :market_history_data)
-      assert length(conn.assigns.market_history_data) == 8
+      assert length(conn.assigns.market_history_data) == 30
     end
   end
 

config/test.exs

@@ -3,4 +3,6 @@ use Mix.Config
 # Print only warnings and errors during test
 config :logger, level: :warn
 
-config :explorer, Explorer.ExchangeRates, source: Explorer.ExchangeRates.Source.TestSource
+config :explorer, Explorer.ExchangeRates,
+  source: Explorer.ExchangeRates.Source.NoOpSource,
+  store: :none

coveralls.json

@@ -1,7 +1,7 @@
 {
   "coverage_options": {
     "treat_no_relevant_lines_as_covered": true,
-    "minimum_coverage": 85
+    "minimum_coverage": 86
   },
   "terminal_options": {
     "file_column_width": 120