Use rake as test runner instead of custom script

Rakefile

@@ -0,0 +1,7 @@
+require "rake/testtask"
+
+task default: "test"
+
+Rake::TestTask.new do |t|
+  t.test_files = FileList['test/test_helper.rb', 'test/**/*_test.rb']
+end

scientist.gemspec

@@ -19,4 +19,5 @@ Gem::Specification.new do |gem|
 
   gem.add_development_dependency "minitest", "~> 5.8"
   gem.add_development_dependency "coveralls", "~> 0.8"
+  gem.add_development_dependency "rake"
 end

script/test

@@ -4,9 +4,4 @@
 set -e
 
 cd $(dirname "$0")/..
-  script/bootstrap && bundle exec ruby -I lib \
-    -e 'require "bundler/setup"' \
-    -e 'require "coveralls"; Coveralls.wear!{ add_filter ".bundle" }' \
-    -e 'require "minitest/autorun"' \
-    -e 'require "scientist"' \
-    -e '(ARGV.empty? ? Dir["test/**/*_test.rb"] : ARGV).each { |f| load f }' -- "$@"
+  script/bootstrap && bundle exec rake test

test/test_helper.rb

@@ -0,0 +1,4 @@
+require "minitest/autorun"
+
+$LOAD_PATH.unshift(File.expand_path(File.join(__dir__, "../lib")))
+require "scientist"