diff --git a/Library/Homebrew/test/utils/curl_spec.rb b/Library/Homebrew/test/utils/curl_spec.rb
index af153426b5..2fe1397b10 100644
--- a/Library/Homebrew/test/utils/curl_spec.rb
+++ b/Library/Homebrew/test/utils/curl_spec.rb
@@ -3,25 +3,61 @@
 
 require "utils/curl"
 
-describe "curl" do
+describe "Utils::Curl" do
   describe "curl_args" do
+    let(:args) { "foo" }
+    let(:user_agent_string) { "Lorem ipsum dolor sit amet" }
+
     it "returns --disable as the first argument when HOMEBREW_CURLRC is not set" do
       # --disable must be the first argument according to "man curl"
-      expect(curl_args("foo").first).to eq("--disable")
+      expect(curl_args(*args).first).to eq("--disable")
     end
 
-    it "doesn't return --disable as the first argument when HOMEBREW_CURLRC is set" do
+    it "doesn't return `--disable` as the first argument when HOMEBREW_CURLRC is set" do
       ENV["HOMEBREW_CURLRC"] = "1"
-      expect(curl_args("foo").first).not_to eq("--disable")
+      expect(curl_args(*args).first).not_to eq("--disable")
     end
 
     it "uses `--retry 3` when HOMEBREW_CURL_RETRIES is unset" do
-      expect(curl_args("foo").join(" ")).to include("--retry 3")
+      expect(curl_args(*args).join(" ")).to include("--retry 3")
     end
 
     it "uses the given value for `--retry` when HOMEBREW_CURL_RETRIES is set" do
       ENV["HOMEBREW_CURL_RETRIES"] = "10"
-      expect(curl_args("foo").join(" ")).to include("--retry 10")
+      expect(curl_args(*args).join(" ")).to include("--retry 10")
+    end
+
+    it "doesn't use `--retry` when `:retry` == `false`" do
+      expect(curl_args(*args, retry: false).join(" ")).not_to include("--retry")
+    end
+
+    it "uses `--retry 3` when `:retry` == `true`" do
+      expect(curl_args(*args, retry: true).join(" ")).to include("--retry 3")
+    end
+
+    it "uses HOMEBREW_USER_AGENT_FAKE_SAFARI when `:user_agent` is `:browser` or `:fake`" do
+      expect(curl_args(*args, user_agent: :browser).join(" "))
+        .to include("--user-agent #{HOMEBREW_USER_AGENT_FAKE_SAFARI}")
+      expect(curl_args(*args, user_agent: :fake).join(" "))
+        .to include("--user-agent #{HOMEBREW_USER_AGENT_FAKE_SAFARI}")
+    end
+
+    it "uses HOMEBREW_USER_AGENT_CURL when `:user_agent` is `:default` or omitted" do
+      expect(curl_args(*args, user_agent: :default).join(" ")).to include("--user-agent #{HOMEBREW_USER_AGENT_CURL}")
+      expect(curl_args(*args, user_agent: nil).join(" ")).to include("--user-agent #{HOMEBREW_USER_AGENT_CURL}")
+      expect(curl_args(*args).join(" ")).to include("--user-agent #{HOMEBREW_USER_AGENT_CURL}")
+    end
+
+    it "uses provided user agent string when `:user_agent` is a `String`" do
+      expect(curl_args(*args, user_agent: user_agent_string).join(" "))
+        .to include("--user-agent #{user_agent_string}")
+    end
+
+    it "uses `--fail` unless `:show_output` is `true`" do
+      expect(curl_args(*args, show_output: false).join(" ")).to include("--fail")
+      expect(curl_args(*args, show_output: nil).join(" ")).to include("--fail")
+      expect(curl_args(*args).join(" ")).to include("--fail")
+      expect(curl_args(*args, show_output: true).join(" ")).not_to include("--fail")
     end
   end
 end