Add spec to test exit hook for Minitest

spec/defaults_spec.rb

@@ -38,4 +38,11 @@ def filtered?(config, filename)
       expect(filtered?(config, "config/environment.rb")).to be
     end
   end
+
+  context "exit hook" do
+    it "uses Minitest if available" do
+      expect { system RbConfig.ruby, "spec/fixtures/frameworks/minitest.rb" }
+        .to output(Regexp.new(Regexp.escape("4 / 5 LOC (80.0%) covered"))).to_stdout_from_any_process
+    end
+  end
 end

spec/fixtures/frameworks/minitest.rb

@@ -0,0 +1,13 @@
+$LOAD_PATH.unshift(File.join(File.dirname(__FILE__), "..", "..", ".."))
+
+require "minitest/autorun"
+require "lib/simplecov"
+SimpleCov.start
+
+require_relative "../app/models/user"
+
+class TestUser < Minitest::Test
+  def test_it_works
+    assert Foo.new
+  end
+end