Convert brew list test to spec.

Library/Homebrew/test/cmd/list_spec.rb

@@ -0,0 +1,14 @@
+describe "brew list", :integration_test do
+  let(:formulae) { %w[bar foo qux] }
+
+  it "prints all installed Formulae" do
+    formulae.each do |f|
+      (HOMEBREW_CELLAR/f/"1.0/somedir").mkpath
+    end
+
+    expect { brew "list" }
+      .to output("#{formulae.join("\n")}\n").to_stdout
+      .and not_to_output.to_stderr
+      .and be_a_success
+  end
+end

Library/Homebrew/test/list_test.rb

@@ -1,13 +0,0 @@
-require "testing_env"
-
-class IntegrationCommandTestList < IntegrationCommandTestCase
-  def test_list
-    formulae = %w[bar foo qux]
-    formulae.each do |f|
-      (HOMEBREW_CELLAR/"#{f}/1.0/somedir").mkpath
-    end
-
-    assert_equal formulae.join("\n"),
-                 cmd("list")
-  end
-end