Add a true integration test that actually executes Bundler (#41)

Before, our CLI tests were doing a significant amount of stubbing to
avoid making external calls to Bundler commands. This limited the value
of these tests. It also made them tedious to write, and required
behind-the-scenes knowledge of when and how the lower-level code called
out to Bundler.

In this PR, I refactored the existing CLI tests so that the stubbing is
done at a higher level: at the `Reporter` API. This makes test setup
easier while still allowing us to write tests to cover various CLI edge
cases, like error handing.

For the primary, "happy path" case, I've created a `CLIIntegrationTest`.
This runs the actual `update-interactive` executable via
`Open3.capture3`, so every layer of the code base is exercised. Most
importantly, Bundler commands themselves are actually executed.

The integration test confirms that when a gem is selected to be updated,
the update really happens. It does this by inspecting the `Gemfile.lock`
to see that the gem version was changed as expected.

I also updated the `mocha` configuration to make stubbing more strict
going forward.

test/bundle_update_interactive/cli_test.rb

@@ -27,8 +27,7 @@ def test_prints_error_in_red_to_stderr_and_exits_with_failure_status
     end
 
     def test_returns_if_no_gems_to_update_and_nothing_withheld
-      empty_report = stub(empty?: true, updatable_gems: {}, withheld_gems: {})
-      Reporter.expects(:new).returns(mock(generate_report: empty_report))
+      stub_report(updatable_gems: {}, withheld_gems: {})
 
       stdout, stderr = capture_io do
         CLI.new.run(argv: [])
@@ -39,17 +38,16 @@ def test_returns_if_no_gems_to_update_and_nothing_withheld
     end
 
     def test_prints_withheld_gems_and_returns_if_nothing_to_update
-      stdout, stderr, status = Dir.chdir(File.expand_path("../fixtures", __dir__)) do
-        VCR.use_cassette("changelog_requests") do
-          unchanged_lockfile = File.read("Gemfile.lock")
-          BundlerCommands.expects(:parse_outdated).returns({ "sqlite3" => "2.0.3" })
-          BundlerCommands.expects(:read_updated_lockfile).returns(unchanged_lockfile)
-          mock_vulnerable_gems([])
-
-          capture_io_and_exit_status do
-            CLI.new.run(argv: [])
-          end
-        end
+      report = stub_report(
+        updatable_gems: {},
+        withheld_gems: {
+          "sqlite3" => build(:outdated_gem, name: "sqlite3", updated_version: "2.0.3", changelog_uri: nil)
+        }
+      )
+      report.expects(:scan_for_vulnerabilities!)
+
+      stdout, stderr, status = capture_io_and_exit_status do
+        CLI.new.run(argv: [])
       end
 
       assert_equal(<<~EXPECTED_STDERR, stderr)
@@ -64,38 +62,19 @@ def test_prints_withheld_gems_and_returns_if_nothing_to_update
       assert_nil(status)
     end
 
-    def test_shows_withheld_gems_and_interactive_list_of_gems_and_updates_the_selected_ones
-      stdout, stderr, status = Dir.chdir(File.expand_path("../fixtures", __dir__)) do
-        VCR.use_cassette("changelog_requests") do
-          updated_lockfile = File.read("Gemfile.lock.updated")
-          BundlerCommands.expects(:parse_outdated).returns({ "sqlite3" => "2.0.3" })
-          BundlerCommands.expects(:read_updated_lockfile).returns(updated_lockfile)
-          BundlerCommands.expects(:update_gems_conservatively).with("addressable", "bigdecimal", "builder")
-          mock_vulnerable_gems([])
-
-          stdin_data = " j j \n" # SPACE,DOWN,SPACE,DOWN,SPACE,ENTER selects first three gems to update
-          capture_io_and_exit_status(stdin_data: stdin_data) do
-            CLI.new.run(argv: [])
-          end
-        end
-      end
+    private
 
-      assert_equal(<<~EXPECTED_STDERR, stderr)
-        Resolving latest gem versions...
-        Checking for security vulnerabilities...
-        Finding changelogs..................
-      EXPECTED_STDERR
-
-      menu, selected_gems = stdout.split("Updating the following gems.")
+    def stub_report(withheld_gems: {}, updatable_gems: {})
+      report = Report.new(
+        current_lockfile: nil,
+        withheld_gems: withheld_gems,
+        updatable_gems: updatable_gems
+      )
 
-      assert_match(/The following gems are being held back and cannot be updated/, menu)
-      assert_match(/sqlite3.*2\.0\.3/, menu)
-
-      assert_equal(3, selected_gems.lines.grep(/→/).count)
-      assert_match(/addressable/, selected_gems)
-      assert_match(/bigdecimal/, selected_gems)
-      assert_match(/builder/, selected_gems)
-      assert_nil(status)
+      reporter = Reporter.new
+      reporter.stubs(:generate_report).returns(report)
+      Reporter.stubs(:new).returns(reporter)
+      report
     end
   end
 end

test/factories/outdated_gems.rb

@@ -3,7 +3,7 @@
 FactoryBot.define do
   factory :outdated_gem, class: "BundleUpdateInteractive::OutdatedGem" do
     current_git_version { nil }
-    current_version { "7.0.3" }
+    current_version { "0.0.1" }
     git_source_uri { nil }
     name { "rails" }
     rubygems_source { true }

test/fixtures/integration/Gemfile

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+source "https://rubygems.org"
+gem "bigdecimal"
+gem "minitest", "~> 5.0.0"
+gem "rake"

test/fixtures/integration/Gemfile.lock

@@ -0,0 +1,18 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    bigdecimal (3.1.7)
+    minitest (5.0.0)
+    rake (12.3.3)
+
+PLATFORMS
+  arm64-darwin-23
+  ruby
+
+DEPENDENCIES
+  bigdecimal
+  minitest (~> 5.0.0)
+  rake
+
+BUNDLED WITH
+   2.5.17

test/integration/cli_integration_test.rb

@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+require "test_helper"
+require "open3"
+require "tmpdir"
+
+module BundleUpdateInteractive
+  class CLIIntegrationIest < Minitest::Test
+    def test_updates_lock_file_based_on_selected_gem_while_honoring_gemfile_requirement
+      out, _gemfile, lockfile = run_bundle_update_interactive(
+        fixture: "integration",
+        argv: [],
+        key_presses: "j \n"
+      )
+
+      assert_includes out, "Color legend:"
+
+      assert_includes out, "3 gems can be updated."
+      assert_includes out, "‣ ⬡ bigdecimal  3.1.7   →"
+      assert_includes out, "  ⬡ minitest    5.0.0   →  5.0.8"
+      assert_includes out, "  ⬡ rake        12.3.3  →"
+
+      assert_includes out, "‣ ⬢ minitest    5.0.0   →  5.0.8"
+
+      assert_includes out, "Updating the following gems."
+      assert_includes out, "minitest  5.0.0  →  5.0.8  :default"
+
+      assert_includes out, "Bundle updated!"
+
+      assert_includes lockfile, <<~LOCK
+        GEM
+          remote: https://rubygems.org/
+          specs:
+            bigdecimal (3.1.7)
+            minitest (5.0.8)
+      LOCK
+      assert_includes lockfile, <<~LOCK
+        DEPENDENCIES
+          bigdecimal
+          minitest (~> 5.0.0)
+      LOCK
+    end
+
+    private
+
+    def run_bundle_update_interactive(fixture:, argv:, key_presses: "\n")
+      command = [
+        { "GEM_HOME" => ENV.fetch("GEM_HOME", nil) },
+        Gem.ruby,
+        "-I",
+        File.expand_path("../../lib", __dir__),
+        File.expand_path("../../exe/bundler-update-interactive", __dir__),
+        *argv
+      ]
+      within_fixture_copy(fixture) do
+        Bundler.with_unbundled_env do
+          out, err, status = Open3.capture3(*command, stdin_data: key_presses)
+          raise "Command failed: #{[out, err].join}" unless status.success?
+
+          [out, File.read("Gemfile"), File.read("Gemfile.lock")]
+        end
+      end
+    end
+
+    def within_fixture_copy(fixture, &block)
+      fixture_path = File.join(File.expand_path("../fixtures", __dir__), fixture)
+      Dir.mktmpdir do |tmp|
+        FileUtils.cp_r(fixture_path, tmp)
+        Dir.chdir(File.join(tmp, File.basename(fixture_path)), &block)
+      end
+    end
+  end
+end

test/support/mocha.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+require "mocha/minitest"
+
+Mocha.configure do |config|
+  config.stubbing_method_on_nil = :prevent
+  config.stubbing_non_existent_method = :prevent
+end

test/test_helper.rb

@@ -3,7 +3,6 @@
 $LOAD_PATH.unshift File.expand_path("../lib", __dir__)
 require "bundle_update_interactive"
 require "minitest/autorun"
-require "mocha/minitest"
 
 BundleUpdateInteractive.pastel = Pastel.new(enabled: true)