Convert brew formula test to spec.

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

@@ -0,0 +1,10 @@
+describe "brew formula", :integration_test do
+  it "prints a given Formula's path" do
+    formula_file = setup_test_formula "testball"
+
+    expect { brew "formula", "testball" }
+      .to output("#{formula_file}\n").to_stdout
+      .and not_to_output.to_stderr
+      .and be_a_success
+  end
+end

Library/Homebrew/test/formula_cmd_test.rb

@@ -1,8 +0,0 @@
-require "testing_env"
-
-class IntegrationCommandTestFormula < IntegrationCommandTestCase
-  def test_formula
-    formula_file = setup_test_formula "testball"
-    assert_equal formula_file.to_s, cmd("formula", "testball")
-  end
-end