test mix coveralls.safe_travis error condition

lib/mix/tasks/build.ex

@@ -19,7 +19,7 @@ if Mix.env() == :test do
     @spec run_formatter([binary()]) :: any()
     def run_formatter(argv) do
       if System.version() >= @required_elixir_version do
-        IO.puts("#{cyan()}#{bright()}Running formatter")
+        Mix.shell().info("#{cyan()}#{bright()}Running formatter")
         Format.run(["--check-equivalent" | argv])
       else
         raise RuntimeError, """

test/mix/tasks_test.exs

@@ -37,10 +37,18 @@ defmodule ExUnit.Mix.Tasks.Receiver.BuildTest do
     end
   end
 
-  test "runs coveralls.safe_travis" do
-    with_mock Travis, run: fn _ -> nil end do
-      SafeTravis.run(["hello"])
-      assert_called(Travis.run(["hello"]))
+  describe "mix coveralls.safe_travis" do
+    test "runs" do
+      with_mock Travis, run: fn _ -> nil end do
+        SafeTravis.run(["hello"])
+        assert_called(Travis.run(["hello"]))
+      end
+    end
+
+    test "catches ExCoveralls.ReportUploadError" do
+      with_mock Travis, run: fn _ -> raise ExCoveralls.ReportUploadError end do
+        assert capture_io(:stderr, fn -> SafeTravis.run(["hello"]) end)
+      end
     end
   end
 end