Add tests

Library/Homebrew/abstract_command.rb

@@ -37,9 +37,9 @@ module Homebrew
     sig { returns(CLI::Args) }
     attr_reader :args
 
-    sig { void }
-    def initialize
-      @args = T.let(CLI::Parser.new(&self.class.parser_block).parse, CLI::Args)
+    sig { params(argv: T::Array[String]).void }
+    def initialize(argv = ARGV.freeze)
+      @args = T.let(CLI::Parser.new(&self.class.parser_block).parse(argv), CLI::Args)
     end
 
     sig { abstract.void }

Library/Homebrew/test/abstract_command_spec.rb

@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+require "abstract_command"
+
+RSpec.describe Homebrew::AbstractCommand do
+  describe "subclasses" do
+    before do
+      cat = Class.new(described_class) do
+        cmd_args do
+          switch "--foo"
+          flag "--bar="
+        end
+        def run; end
+      end
+      stub_const("Cat", cat)
+    end
+
+    describe "parsing args" do
+      it "parses valid args" do
+        expect { Cat.new(["--foo"]).run }.not_to raise_error
+      end
+
+      it "allows access to args" do
+        expect(Cat.new(["--bar", "baz"]).args[:bar]).to eq("baz")
+      end
+
+      it "raises on invalid args" do
+        expect { Cat.new(["--bat"]) }.to raise_error(OptionParser::InvalidOption)
+      end
+    end
+
+    describe "command names" do
+      it "has a default command name" do
+        expect(Cat.command_name).to eq("cat")
+      end
+
+      it "can lookup command" do
+        expect(described_class.command("cat")).to be(Cat)
+      end
+
+      describe "when command name is overridden" do
+        before do
+          tac = Class.new(described_class) do
+            def self.command_name = "t-a-c"
+            def run; end
+          end
+          stub_const("Tac", tac)
+        end
+
+        it "can be looked up by command name" do
+          expect(described_class.command("t-a-c")).to be(Tac)
+        end
+      end
+    end
+  end
+end

Library/Homebrew/test/abstract_command_spec.rbi

@@ -0,0 +1,4 @@
+# typed: strict
+
+class Cat < Homebrew::AbstractCommand; end
+class Tac < Homebrew::AbstractCommand; end