Convert `brew desc` test to spec.

Library/Homebrew/test/cmd/desc_spec.rb

+describe "brew desc", :integration_test do
+  let(:desc_cache) { HOMEBREW_CACHE/"desc_cache.json" }
+
+  it "shows a given Formula's description" do
+    setup_test_formula "testball"
+
+    expect { brew "desc", "testball" }
+      .to output("testball: Some test\n").to_stdout
+      .and not_to_output.to_stderr
+      .and be_a_success
+  end
+
+  it "fails when both --search and --name are specified" do
+    expect { brew "desc", "--search", "--name" }
+      .to output(/Pick one, and only one/).to_stderr
+      .and not_to_output.to_stdout
+      .and be_a_failure
+  end
+
+  describe "--search" do
+    it "fails when no search term is given" do
+      expect { brew "desc", "--search" }
+        .to output(/You must provide a search term/).to_stderr
+        .and not_to_output.to_stdout
+        .and be_a_failure
+    end
+  end
+
+  describe "--description" do
+    it "creates a description cache" do
+      expect(desc_cache).not_to exist
+
+      shutup do
+        expect { brew "desc", "--description", "testball" }.to be_a_success
+      end
+
+      expect(desc_cache).to exist
+    end
+  end
+end

Library/Homebrew/test/desc_test.rb

-require "testing_env"
-
-class IntegrationCommandTestDesc < IntegrationCommandTestCase
-  def test_desc
-    setup_test_formula "testball"
-
-    assert_equal "testball: Some test", cmd("desc", "testball")
-    assert_match "Pick one, and only one", cmd_fail("desc", "--search", "--name")
-    assert_match "You must provide a search term", cmd_fail("desc", "--search")
-
-    desc_cache = HOMEBREW_CACHE/"desc_cache.json"
-    refute_predicate desc_cache, :exist?, "Cached file should not exist"
-
-    cmd("desc", "--description", "testball")
-    assert_predicate desc_cache, :exist?, "Cached file should not exist"
-  end
-end