Split railties suite in half

.travis.yml

@@ -41,7 +41,8 @@ env:
   global:
     - "JRUBY_OPTS='--dev -J-Xmx1024M'"
   matrix:
-    - "GEM=railties"
+    - "GEM=railties:1"
+    - "GEM=railties:2"
     - "GEM=ap,ac"
     - "GEM=am,amo,as,av,aj,ast"
     - "GEM=as PRESERVE_TIMEZONES=1"

ci/travis.rb

@@ -78,10 +78,15 @@ def tasks
       end
       tasks
     else
-      ["test", ("isolated" if isolated?), ("integration" if integration?), ("ujs" if ujs?)].compact.join(":")
+      ["test", ("isolated" if isolated?), ("integration" if integration?), ("ujs" if ujs?), subset].compact.join(":")
     end
   end
 
+  def subset
+    n = component.split(":").last
+    n if n =~ /\A\d+\z/
+  end
+
   def key
     key = [gem]
     key << adapter if activerecord?
@@ -166,7 +171,7 @@ def run_bug_report_templates
     next if gem == "av:ujs" && isolated
     next if gem == "guides" && isolated
     next if gem =~ /:integration/ && isolated
-    next if gem == "railties" && isolated
+    next if gem =~ /railties:/ && isolated
 
     build = Build.new(gem, isolated: isolated)
     failures << build.key unless build.run!

railties/Rakefile

@@ -9,8 +9,7 @@ task :package
 desc "Run all unit tests"
 task test: "test:isolated"
 
-namespace :test do
-  task :isolated do
+run_isolated_tests = lambda do |files|
   dash_i = [
     "test",
     "lib",
@@ -28,11 +27,7 @@ namespace :test do
   require "bundler/setup" unless defined?(Bundler)
   require "active_support"
 
-    failing_files = []
-
-    dirs = (ENV["TEST_DIR"] || ENV["TEST_DIRS"] || "**").split(",")
-    test_files = dirs.map { |dir| "test/#{dir}/*_test.rb" }
-    Dir[*test_files].each do |file|
+  failing_files = files.reject do |file|
     next true if file.start_with?("test/fixtures/")
 
     fake_command = Shellwords.join([
@@ -52,9 +47,7 @@ namespace :test do
       load file
     }
 
-      unless $?.success?
-        failing_files << file
-      end
+    $?.success?
   end
 
   unless failing_files.empty?
@@ -67,6 +60,30 @@ namespace :test do
 
     raise "Failure in isolated test runner"
   end
+end
+
+_test_files = nil
+test_files = lambda do
+  _test_files ||= Dir[*
+    (ENV["TEST_DIR"] || ENV["TEST_DIRS"] || "**").
+      split(",").
+      map { |dir| "test/#{dir}/*_test.rb" }
+  ]
+end
+
+split_filter = lambda { |file| file =~ /test\/application\// }
+
+namespace :test do
+  task "1" do
+    run_isolated_tests.call test_files.call.select(&split_filter)
+  end
+
+  task "2" do
+    run_isolated_tests.call test_files.call.reject(&split_filter)
+  end
+
+  task :isolated do
+    run_isolated_tests.call test_files.call
   end
 end