feat: add linux tests

Library/Homebrew/os/linux.rb

@@ -63,10 +63,23 @@ module OS
     def self.languages
       return @languages if @languages.present?
 
-      os_langs = Utils.popen_read("localectl", "list-locales")
-      os_langs = os_langs.scan(/[^ \n"(),]+/).map { |item| item.split(".").first.tr("_", "-") }
+      locale_variables = ENV.keys.grep(/^(?:LC_\S+|LANG|LANGUAGE)\Z/).sort
+      ctl_ret = Utils.popen_read("localectl", "list-locales")
+      if ctl_ret.present?
+        list = ctl_ret.scan(/[^ \n"(),]+/)
+      elsif locale_variables.present?
+        keys = locale_variables.select { |var| ENV.fetch(var) }
+        list = keys.map { |key| ENV.fetch(key) }
+      else
+        list = ["en_US.utf8"]
+      end
 
-      @languages = os_langs
+      @languages = list.map { |item| item.split(".").first.tr("_", "-") }
+    end
+
+    sig { returns(T.nilable(String)) }
+    def self.language
+      languages.first
     end
   end
 end

Library/Homebrew/test/os/linux_spec.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+require "locale"
+require "os/linux"
+
+RSpec.describe OS::Linux do
+  describe "::languages", :needs_linux do
+    it "returns a list of all languages" do
+      expect(described_class.languages).not_to be_empty
+    end
+  end
+
+  describe "::language", :needs_linux do
+    it "returns the first item from #languages" do
+      expect(described_class.language).to eq(described_class.languages.first)
+    end
+  end
+
+  describe "::'os_version'", :needs_linux do
+    it "returns the OS version" do
+      expect(described_class.os_version).not_to be_empty
+    end
+  end
+
+  describe "::'wsl?'" do
+    it "returns the WSL state" do
+      expect(described_class.wsl?).to be(false)
+    end
+  end
+
+  describe "::'wsl_version'", :needs_linux do
+    it "returns the WSL version" do
+      expect(described_class.wsl_version).to match(Version::NULL)
+    end
+  end
+end