'brew tests' optional coverage measure added

Closes Homebrew/homebrew#41890.

Signed-off-by: Baptiste Fontaine <batifon@yahoo.fr>

.gitignore

@@ -17,6 +17,7 @@
 /Library/Homebrew/test/.bundle
 /Library/Homebrew/test/bin
 /Library/Homebrew/test/vendor
+/Library/Homebrew/test/coverage
 /Library/LinkedKegs
 /Library/PinnedKegs
 /Library/Taps

Library/Homebrew/cmd/tests.rb

@@ -2,6 +2,7 @@ module Homebrew
   def tests
     (HOMEBREW_LIBRARY/"Homebrew/test").cd do
       ENV["TESTOPTS"] = "-v" if ARGV.verbose?
+      ENV["HOMEBREW_TESTS_COVERAGE"] = "1" if ARGV.flag? "--coverage"
       Homebrew.install_gem_setup_path! "bundler"
       quiet_system("bundle", "check") || \
         system("bundle", "install", "--path", "vendor/bundle")

Library/Homebrew/test/Gemfile

@@ -3,3 +3,4 @@ source "https://rubygems.org"
 gem "mocha", "~> 1.1"
 gem "minitest", "~> 5.3"
 gem "rake", "~> 10.3"
+gem "simplecov", "~> 0.10.0", :require => false

Library/Homebrew/test/Gemfile.lock

@@ -1,11 +1,18 @@
 GEM
   remote: https://rubygems.org/
   specs:
+    docile (1.1.5)
+    json (1.8.3)
     metaclass (0.0.4)
     minitest (5.7.0)
     mocha (1.1.0)
       metaclass (~> 0.0.1)
     rake (10.4.2)
+    simplecov (0.10.0)
+      docile (~> 1.1.0)
+      json (~> 1.8)
+      simplecov-html (~> 0.10.0)
+    simplecov-html (0.10.0)
 
 PLATFORMS
   ruby
@@ -14,3 +21,4 @@ DEPENDENCIES
   minitest (~> 5.3)
   mocha (~> 1.1)
   rake (~> 10.3)
+  simplecov (~> 0.10.0)

Library/Homebrew/test/testing_env.rb

@@ -1,6 +1,22 @@
 $:.unshift File.expand_path("../..", __FILE__)
 $:.unshift File.expand_path("../lib", __FILE__)
 
+# This must be at the top
+if ENV["HOMEBREW_TESTS_COVERAGE"]
+  require "simplecov"
+  SimpleCov.start do
+    tests_path = File.dirname(__FILE__)
+
+    minimum_coverage 50
+    coverage_dir File.expand_path("#{tests_path}/coverage")
+    root File.expand_path("#{tests_path}/..")
+
+    add_filter "Homebrew/test"
+    add_filter "vendor/bundle"
+    add_filter "Homebrew/vendor"
+  end
+end
+
 require "global"
 
 # Test environment setup