Run all tests by default; ability to run tests by arbitrary path(s)

Similar to RSpec and the Rails test runner, this commit adds a feature
where the `mt` executable can run multiple tests at once based on
command line arguments. When executed with no args, it now runs all
tests by default.

```sh
# Run all tests
bin/mt

# Run a specific test file
bin/mt test/cli_test.rb

# Run a directory of tests
bin/mt test/commands

# Run many tests/directories at once
bin/mt test/cli_test.rb test/commands
```

lib/mighty_test/cli.rb

@@ -1,6 +1,7 @@
 module MightyTest
   class CLI
-    def initialize(env: ENV, option_parser: OptionParser.new, runner: MinitestRunner.new)
+    def initialize(file_system: FileSystem.new, env: ENV, option_parser: OptionParser.new, runner: MinitestRunner.new)
+      @file_system = file_system
       @env = env.to_h
       @option_parser = option_parser
       @runner = runner
@@ -26,7 +27,7 @@ def run(argv: ARGV)
 
     private
 
-    attr_reader :env, :path_args, :extra_args, :options, :option_parser, :runner
+    attr_reader :file_system, :env, :path_args, :extra_args, :options, :option_parser, :runner
 
     def print_help
       # Minitest already prints the `-h, --help` option, so omit mighty_test's
@@ -44,14 +45,33 @@ def run_test_by_line_number
       test_name = TestParser.new(path).test_name_at_line(line.to_i)
 
       if test_name
-        runner.run_inline_and_exit!(path, args: ["-n", "/^#{Regexp.quote(test_name)}$/"] + extra_args)
+        run_tests_and_exit!(path, flags: ["-n", "/^#{Regexp.quote(test_name)}$/"])
       else
-        runner.run_inline_and_exit!(args: extra_args)
+        run_tests_and_exit!
       end
     end
 
     def run_tests_by_path
-      runner.run_inline_and_exit!(*path_args, args: extra_args)
+      test_paths = find_test_paths
+      run_tests_and_exit!(*test_paths)
+    end
+
+    def find_test_paths
+      return file_system.find_test_paths if path_args.empty?
+
+      path_args.flat_map do |path|
+        if Dir.exist?(path)
+          file_system.find_test_paths(path)
+        elsif File.exist?(path)
+          [path]
+        else
+          raise ArgumentError, "#{path} does not exist"
+        end
+      end
+    end
+
+    def run_tests_and_exit!(*test_paths, flags: [])
+      runner.run_inline_and_exit!(*test_paths, args: extra_args + flags)
     end
 
     def handle_exception(e) # rubocop:disable Naming/MethodParameterName

lib/mighty_test/file_system.rb

@@ -12,5 +12,10 @@ def find_matching_test_file(path)
       test_path = path[%r{^(?:app|lib)/(.+)\.[^\.]+$}, 1].then { "test/#{_1}_test.rb" }
       test_path if test_path && File.exist?(test_path)
     end
+
+    def find_test_paths(directory="test")
+      glob = File.join(directory, "**/*_test.rb")
+      Dir[glob]
+    end
   end
 end

lib/mighty_test/option_parser.rb

@@ -6,7 +6,8 @@ def initialize
       @parser = ::OptionParser.new do |op|
         op.require_exact = true
         op.banner = <<~BANNER
-          Usage: mt <test file>...
+          Usage: mt
+                 mt [test file...] [test dir...]
                  mt --watch
 
         BANNER

test/mighty_test/cli_test.rb

@@ -2,6 +2,8 @@
 
 module MightyTest
   class CLITest < Minitest::Test
+    include FixturesPath
+
     def test_help_flag_prints_usage_and_minitest_options
       result = cli_run(argv: ["--help"])
 
@@ -27,15 +29,96 @@ def test_version_flag_prints_version
       assert_equal(VERSION, result.stdout.chomp)
     end
 
+    def test_with_no_args_runs_all_tests_in_the_test_directory
+      with_fake_minitest_runner do |runner, executed_tests|
+        cli_run(argv: [], chdir: fixtures_path.join("rails_project"), runner:)
+
+        assert_equal(
+          %w[
+            test/helpers/users_helper_test.rb
+            test/models/account_test.rb
+            test/models/user_test.rb
+            test/system/users_system_test.rb
+          ],
+          executed_tests.sort
+        )
+      end
+    end
+
+    def test_with_a_directory_arg_runs_all_test_files_in_that_directory
+      with_fake_minitest_runner do |runner, executed_tests|
+        cli_run(argv: ["test/models"], chdir: fixtures_path.join("rails_project"), runner:)
+
+        assert_equal(
+          %w[
+            test/models/account_test.rb
+            test/models/user_test.rb
+          ],
+          executed_tests.sort
+        )
+      end
+    end
+
+    def test_with_a_mixture_of_file_and_directory_args_runs_all_matching_tests
+      with_fake_minitest_runner do |runner, executed_tests|
+        cli_run(argv: %w[test/system test/models/user_test.rb], chdir: fixtures_path.join("rails_project"), runner:)
+
+        assert_equal(
+          %w[
+            test/models/user_test.rb
+            test/system/users_system_test.rb
+          ],
+          executed_tests.sort
+        )
+      end
+    end
+
+    def test_with_explict_file_args_runs_those_files_regardless_of_whether_they_appear_to_be_tests
+      with_fake_minitest_runner do |runner, executed_tests|
+        cli_run(argv: ["app/models/user.rb"], chdir: fixtures_path.join("rails_project"), runner:)
+
+        assert_equal(
+          %w[
+            app/models/user.rb
+          ],
+          executed_tests.sort
+        )
+      end
+    end
+
+    def test_with_directory_args_only_runs_files_that_appear_to_be_tests
+      with_fake_minitest_runner do |runner, executed_tests|
+        cli_run(argv: ["app/models"], chdir: fixtures_path.join("rails_project"), runner:)
+
+        assert_empty(executed_tests)
+      end
+    end
+
+    def test_with_non_existent_path_raises_an_error
+      error = assert_raises(ArgumentError) do
+        cli_run(argv: ["test/models/non_existent_test.rb"], chdir: fixtures_path.join("rails_project"))
+      end
+
+      assert_includes(error.message, "test/models/non_existent_test.rb does not exist")
+    end
+
     private
 
-    def cli_run(argv:, env: {}, stdin: nil, raise_on_failure: true)
+    def with_fake_minitest_runner
+      executed_tests = []
+      runner = MinitestRunner.new
+      runner.stub(:run_inline_and_exit!, ->(*test_files, **) { executed_tests.append(*test_files.flatten) }) do
+        yield(runner, executed_tests)
+      end
+    end
+
+    def cli_run(argv:, env: {}, chdir: ".", runner: nil, raise_on_failure: true)
       exitstatus = true
-      orig_stdin = $stdin
-      $stdin = StringIO.new(stdin) if stdin
 
       stdout, stderr = capture_io do
-        CLI.new(env:).run(argv:)
+        Dir.chdir(chdir) do
+          CLI.new(**{ env:, runner: }.compact).run(argv:)
+        end
       rescue SystemExit => e
         exitstatus = e.status
       end
@@ -44,8 +127,6 @@ def cli_run(argv:, env: {}, stdin: nil, raise_on_failure: true)
       raise "CLI exited with status: #{exitstatus}" if raise_on_failure && result.failure?
 
       result
-    ensure
-      $stdin = orig_stdin
     end
   end
 end