Convert Emoji test to spec.

Library/Homebrew/test/emoji_spec.rb

@@ -0,0 +1,16 @@
+require "emoji"
+
+describe Emoji do
+  describe "#install_badge" do
+    subject { described_class.install_badge }
+
+    it "returns 🍺 by default" do
+      expect(subject).to eq "🍺"
+    end
+
+    it "returns the contents of HOMEBREW_INSTALL_BADGE if set" do
+      ENV["HOMEBREW_INSTALL_BADGE"] = "foo"
+      expect(subject).to eq "foo"
+    end
+  end
+end

Library/Homebrew/test/emoji_test.rb

@@ -1,11 +0,0 @@
-require "testing_env"
-require "emoji"
-
-class EmojiTest < Homebrew::TestCase
-  def test_install_badge
-    assert_equal "🍺", Emoji.install_badge
-
-    ENV["HOMEBREW_INSTALL_BADGE"] = "foo"
-    assert_equal "foo", Emoji.install_badge
-  end
-end