Repair tests for exchange rates/know tokens sorce by addind mock for headers function

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

@@ -61,7 +61,7 @@ defmodule Explorer.ExchangeRates.Source do
 
   @callback source_url(String.t()) :: String.t() | :ignore
 
-  @callback headers() :: [any]
+  @callback headers :: [any]
 
   def headers do
     [{"Content-Type", "application/json"}]

apps/explorer/lib/explorer/known_tokens/source.ex

@@ -19,6 +19,8 @@ defmodule Explorer.KnownTokens.Source do
   """
   @callback source_url() :: String.t()
 
+  @callback headers() :: [any()]
+
   @spec known_tokens_source() :: module()
   defp known_tokens_source do
     config(:source) || Explorer.KnownTokens.Source.MyEtherWallet

apps/explorer/lib/explorer/known_tokens/source/my_ether_wallet.ex

@@ -11,4 +11,9 @@ defmodule Explorer.KnownTokens.Source.MyEtherWallet do
   def source_url do
     "https://raw.githubusercontent.com/kvhnuke/etherwallet/mercury/app/scripts/tokens/ethTokens.json"
   end
+
+  @impl Source
+  def headers do
+    []
+  end
 end

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

@@ -54,6 +54,7 @@ defmodule Explorer.ExchangeRatesTest do
     state = %{}
 
     expect(TestSource, :format_data, fn _ -> [Token.null()] end)
+    expect(TestSource, :headers, fn -> [] end)
     set_mox_global()
 
     assert {:noreply, ^state} = ExchangeRates.handle_info(:update, state)
@@ -102,6 +103,7 @@ defmodule Explorer.ExchangeRatesTest do
       state = %{}
 
       expect(TestSource, :format_data, fn _ -> [Token.null()] end)
+      expect(TestSource, :headers, fn -> [] end)
       set_mox_global()
 
       assert {:noreply, ^state} = ExchangeRates.handle_info({nil, {:error, "some error"}}, state)

apps/explorer/test/explorer/known_tokens/known_tokens_test.exs

@@ -51,6 +51,7 @@ defmodule Explorer.KnownTokensTest do
     end)
 
     stub(TestSource, :source_url, fn -> "http://localhost:#{bypass.port}" end)
+    stub(TestSource, :headers, fn -> [] end)
 
     KnownTokens.init([])
     state = %{}
@@ -89,6 +90,7 @@ defmodule Explorer.KnownTokensTest do
       end)
 
       stub(TestSource, :source_url, fn -> "http://localhost:#{bypass.port}" end)
+      stub(TestSource, :headers, fn -> [] end)
 
       state = %{}