Add tests.

Library/Homebrew/test/service_spec.rb

@@ -587,6 +587,44 @@ describe Homebrew::Service do
       EOS
       expect(plist).to eq(plist_expect)
     end
+
+    it "expands paths" do
+      f = stub_formula do
+        service do
+          run opt_bin/"beanstalkd"
+          working_dir "~"
+        end
+      end
+
+      plist = f.service.to_plist
+      plist_expect = <<~EOS
+        <?xml version="1.0" encoding="UTF-8"?>
+        <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+        <plist version="1.0">
+        <dict>
+        \t<key>Label</key>
+        \t<string>homebrew.mxcl.formula_name</string>
+        \t<key>LimitLoadToSessionType</key>
+        \t<array>
+        \t\t<string>Aqua</string>
+        \t\t<string>Background</string>
+        \t\t<string>LoginWindow</string>
+        \t\t<string>StandardIO</string>
+        \t\t<string>System</string>
+        \t</array>
+        \t<key>ProgramArguments</key>
+        \t<array>
+        \t\t<string>#{HOMEBREW_PREFIX}/opt/formula_name/bin/beanstalkd</string>
+        \t</array>
+        \t<key>RunAtLoad</key>
+        \t<true/>
+        \t<key>WorkingDirectory</key>
+        \t<string>#{Dir.home}</string>
+        </dict>
+        </plist>
+      EOS
+      expect(plist).to eq(plist_expect)
+    end
   end
 
   describe "#to_systemd_unit" do
@@ -657,6 +695,30 @@ describe Homebrew::Service do
       EOS
       expect(unit).to eq(unit_expect.strip)
     end
+
+    it "expands paths" do
+      f = stub_formula do
+        service do
+          run opt_bin/"beanstalkd"
+          working_dir "~"
+        end
+      end
+
+      unit = f.service.to_systemd_unit
+      unit_expect = <<~EOS
+        [Unit]
+        Description=Homebrew generated unit for formula_name
+
+        [Install]
+        WantedBy=default.target
+
+        [Service]
+        Type=simple
+        ExecStart=#{HOMEBREW_PREFIX}/opt/#{name}/bin/beanstalkd
+        WorkingDirectory=#{Dir.home}
+      EOS
+      expect(unit).to eq(unit_expect.strip)
+    end
   end
 
   describe "#to_systemd_timer" do