Convert `brew edit` test to spec.

Library/Homebrew/test/dev-cmd/edit_spec.rb

+describe "brew edit", :integration_test do
+  it "opens a given Formula in an editor" do
+    HOMEBREW_REPOSITORY.cd do
+      shutup do
+        system "git", "init"
+      end
+    end
+
+    setup_test_formula "testball"
+
+    expect { brew "edit", "testball", "HOMEBREW_EDITOR" => "/bin/cat" }
+      .to output(/# something here/).to_stdout
+      .and not_to_output.to_stderr
+      .and be_a_success
+  end
+end

Library/Homebrew/test/edit_test.rb

-require "testing_env"
-
-class IntegrationCommandTestEdit < IntegrationCommandTestCase
-  def test_edit
-    (HOMEBREW_REPOSITORY/".git").mkpath
-    setup_test_formula "testball"
-
-    assert_match "# something here",
-                 cmd("edit", "testball", "HOMEBREW_EDITOR" => "/bin/cat")
-  end
-end