Add better quality test coverage for formatter functions

Remove redundant function declaration since nil is already handled

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

@@ -14,8 +14,6 @@ defmodule ExplorerWeb.ChainView do
     end
   end
 
-  def format_exchange_rate(%Token{usd_value: nil}), do: nil
-
   def format_exchange_rate(%Token{usd_value: usd_value}) do
     usd_value
     |> USD.from()

apps/explorer_web/test/explorer_web/views/chain_view_test.exs

@@ -1,3 +1,33 @@
 defmodule ExplorerWeb.ChainViewTest do
   use ExplorerWeb.ConnCase, async: true
+
+  alias Explorer.ExchangeRates.Token
+  alias ExplorerWeb.ChainView
+
+  describe "format_exchange_rate/1" do
+    test "returns a formatted usd value from a `Token`'s usd_value" do
+      token = %Token{usd_value: Decimal.new(5.45)}
+
+      assert "$5.45 USD" == ChainView.format_exchange_rate(token)
+      assert nil == ChainView.format_exchange_rate(%Token{usd_value: nil})
+    end
+  end
+
+  describe "format_volume_24h/1" do
+    test "returns a formatted usd value from a `Token`'s volume_24h_usd" do
+      token = %Token{volume_24h_usd: Decimal.new(5.456)}
+
+      assert "$5.456 USD" == ChainView.format_volume_24h(token)
+      assert nil == ChainView.format_volume_24h(%Token{volume_24h_usd: nil})
+    end
+  end
+
+  describe "format_market_cap/1" do
+    test "returns a formatted usd value from a `Token`'s market_cap_usd" do
+      token = %Token{market_cap_usd: Decimal.new(5.4)}
+
+      assert "$5.40 USD" == ChainView.format_market_cap(token)
+      assert nil == ChainView.format_market_cap(%Token{market_cap_usd: nil})
+    end
+  end
 end