Add unit test for previous commit

Author: okkez

spec/bundler/installer/gem_installer_spec.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+require "spec_helper"
+require "bundler/installer/gem_installer"
+
+RSpec.describe Bundler::GemInstaller do
+  let(:installer) { instance_double("Installer") }
+  let(:spec_source) { instance_double("SpecSource") }
+  let(:spec) { instance_double("Specification", :name => "dummy", :version => "0.0.1", :loaded_from => "dummy", :source => spec_source) }
+
+  subject { described_class.new(spec, installer) }
+
+  context "spec_settings is nil" do
+    it "invokes install method with empty build_args" do
+      allow(spec_source).to receive(:install).with(spec, :force => false, :ensure_builtin_gems_cached => false, :build_args => [])
+      subject.install_from_spec
+    end
+  end
+
+  context "spec_settings is build option" do
+    it "invokes install method with build_args" do
+      allow(Bundler.settings).to receive(:[]).with(:bin)
+      allow(Bundler.settings).to receive(:[]).with("build.dummy").and_return("--with-dummy-config=dummy")
+      allow(spec_source).to receive(:install).with(spec, :force => false, :ensure_builtin_gems_cached => false, :build_args => ["--with-dummy-config=dummy"])
+      subject.install_from_spec
+    end
+  end
+end