tests: add groups and project name to coverage

Groups make it easier to get an overview of the coverage without having
to scan through a single very long list of files. They also display a
possibly helpful per-group coverage.

The project name is normally derived from the `root` directory which
happens to be `Library` in our case, thus make it explicitly `Homebrew`.

Closes Homebrew/homebrew#49303.

Signed-off-by: Martin Afanasjew <martin@afanasjew.de>

Library/Homebrew/test/.simplecov

@@ -18,6 +18,19 @@ SimpleCov.start do
   unless ENV["HOMEBREW_INTEGRATION_TEST"]
     track_files "#{SimpleCov.root}/**/*.rb"
   end
+
+  # Add groups and the proper project name to the output.
+  project_name "Homebrew"
+  add_group "Commands", %w[/Homebrew/cmd/ /Homebrew/dev-cmd/]
+  add_group "Extensions", "/Homebrew/extend/"
+  add_group "OS", "/Homebrew/os/"
+  add_group "Requirements", "/Homebrew/requirements/"
+  add_group "Scripts", %w[
+    /brew.rb
+    /Homebrew/build.rb
+    /Homebrew/postinstall.rb
+    /Homebrew/test.rb
+  ]
 end
 
 if ENV["HOMEBREW_INTEGRATION_TEST"]