Convert brew --cache test to spec.

Library/Homebrew/test/cache_formula_test.rb

@@ -1,8 +0,0 @@
-require "testing_env"
-
-class IntegrationCommandTestCacheFormula < IntegrationCommandTestCase
-  def test_cache_formula
-    assert_match %r{#{HOMEBREW_CACHE}/testball-},
-                 cmd("--cache", testball)
-  end
-end

Library/Homebrew/test/cache_test.rb

@@ -1,8 +0,0 @@
-require "testing_env"
-
-class IntegrationCommandTestCache < IntegrationCommandTestCase
-  def test_cache
-    assert_equal HOMEBREW_CACHE.to_s,
-                 cmd("--cache")
-  end
-end

Library/Homebrew/test/cmd/--cache_spec.rb

@@ -0,0 +1,15 @@
+describe "brew --cache", :integration_test do
+  it "print the location of Homebrew's cache when no argument is given" do
+    expect { brew "--cache" }
+      .to output("#{HOMEBREW_CACHE}\n").to_stdout
+      .and not_to_output.to_stderr
+      .and be_a_success
+  end
+
+  it "prints all cache files for a given Formula" do
+    expect { brew "--cache", testball }
+      .to output(%r{#{HOMEBREW_CACHE}/testball-}).to_stdout
+      .and not_to_output.to_stderr
+      .and be_a_success
+  end
+end