Create add and remove subcommands for brew bundle

cmd/bundle.rb

@@ -107,6 +107,11 @@ def bundle
             zap:    args.zap?,
           )
         end
+      when "add"
+        Bundle::Commands::Add.run(
+          global: args.global?,
+          file:   args.file,
+        )
       when "dump"
         Bundle::Commands::Dump.run(
           global:     args.global?,

lib/bundle/commands/add.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+module Bundle
+  module Commands
+    module Add
+      module_function
+
+      def run(*args, global: false, file: nil)
+        raise UsageError, "No arguments were specified!" if args.blank?
+
+        type = :brew # default to brew
+        name = args.first # only support one formula at a time for now
+        options = {} # we don't currently support passing options
+
+        # parse the relevant Brewfile
+        dsl = Bundle::Dsl.new(Brewfile.read(global: global, file: file))
+
+        # check each of the entries in the specified Brewfile
+        dsl.entries.each do |entry|
+          # raise an error if the entry already exists in the Brewfile
+          # this could also be a noop, or print a friendly message
+          opoo "'#{name}' already exists in Brewfile."
+          raise RuntimeError if entry.name == name
+        end
+
+        dsl.brew(name, options)
+        # execute brew bundle
+        # execute brew bundle dump
+      end
+    end
+  end
+end

spec/bundle/commands/add_command_spec.rb

@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+describe Bundle::Commands::Add do
+  context "when a Brewfile is not found" do
+    it "raises an error" do
+      expect { described_class.run("wget") }.to raise_error(RuntimeError)
+    end
+  end
+
+  context "when a Brewfile is found" do
+    before do
+      allow_any_instance_of(Pathname).to receive(:read)
+        .and_return("brew 'openssl'")
+    end
+
+    context "when no arguments are passed" do
+      it "raises an error" do
+        expect { described_class.run }.to raise_error(UsageError)
+      end
+    end
+
+    context "the formula is not in the Brewfile" do
+      it "does not raise an error" do
+        expect { described_class.run("wget") }.not_to raise_error
+      end
+
+      it "adds the formula to the Brewfile" do
+        # TODO
+      end
+    end
+
+    context "the formula is in the Brewfile" do
+      before do
+        allow_any_instance_of(Pathname).to receive(:read)
+          .and_return("brew 'openssl'\nbrew 'wget'")
+      end
+
+      it "raises an error" do
+        expect { described_class.run("wget") }.to raise_error(RuntimeError)
+      end
+    end
+  end
+end