Add test for RailsStats::CodeStatistics#to_s and set up rake to run tests by default

Considering there were no tests, I decided to use minitest and set it up to run by default (`bundle exec rake`)

I added a simple test to make sure that `to_s` is working as expected

Author: etagwerker

Rakefile

@@ -1 +1,12 @@
-require "rails_stats"
+# frozen_string_literal: true
+
+require "bundler/gem_tasks"
+require "rake/testtask"
+
+Rake::TestTask.new do |task|
+  task.libs.push "lib"
+  task.libs.push "test"
+  task.pattern = "test/**/*_test.rb"
+end
+
+task default: %i[test]

test/lib/rails_stats/code_statistics_test.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+describe RailsStats::CodeStatistics do
+  describe "#to_s" do
+    TABLE = <<~EOS
+    +----------------------+-------+-------+---------+---------+-----+-------+
+    | Name                 | Lines |   LOC | Classes | Methods | M/C | LOC/M |
+    +----------------------+-------+-------+---------+---------+-----+-------+
+    | Mailers              |     4 |     4 |       1 |       0 |   0 |     0 |
+    | Models               |     3 |     3 |       1 |       0 |   0 |     0 |
+    | Javascripts          |    27 |     7 |       0 |       0 |   0 |     0 |
+    | Jobs                 |     7 |     2 |       1 |       0 |   0 |     0 |
+    | Controllers          |     3 |     3 |       1 |       0 |   0 |     0 |
+    | Helpers              |     3 |     3 |       0 |       0 |   0 |     0 |
+    | Channels             |     8 |     8 |       2 |       0 |   0 |     0 |
+    | Configuration        |   417 |   111 |       1 |       0 |   0 |     0 |
+    +----------------------+-------+-------+---------+---------+-----+-------+
+    | Total                |   472 |   141 |       7 |       0 |   0 |     0 |
+    +----------------------+-------+-------+---------+---------+-----+-------+
+      Code LOC: 141     Test LOC: 0     Code to Test Ratio: 1:0.0
+
+    EOS
+
+    it "outputs useful stats for a Rails project" do
+      root_directory = File.absolute_path("./test/dummy")
+      assert_output(TABLE) do
+        RailsStats::CodeStatistics.new(root_directory).to_s
+      end
+    end
+  end
+end

test/test_helper.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+require "byebug"
+
+require "minitest/autorun"
+require "minitest/pride"
+require "minitest/around/spec"
+
+require "rails_stats/all"