Make file update checker tests more resilient on Windows

Without the `wdm` gem, it appears that `listen` keeps an open handle to
each of these files, causing them not to be removed when the tempdir
tries to clean iteslf up, and then directory to fail to unlink. In
addition to fixing that particular failure, we now construct OS agnostic
paths, and capture exceptions if the directory fails to unlink so that
minitest will report it rather than crash

Gemfile

@@ -129,3 +129,4 @@ end
 # A gem necessary for Active Record tests with IBM DB.
 gem 'ibm_db' if ENV['IBM_DB']
 gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]
+gem 'wdm', '>= 0.1.0', platforms: [:mingw, :mswin, :x64_mingw, :mswin64]

Gemfile.lock

@@ -265,6 +265,7 @@ GEM
     w3c_validators (1.2)
       json
       nokogiri
+    wdm (0.1.1)
     websocket-driver (0.6.3)
       websocket-extensions (>= 0.1.0)
     websocket-extensions (0.1.2)
@@ -323,6 +324,7 @@ DEPENDENCIES
   tzinfo-data
   uglifier (>= 1.3.0)
   w3c_validators
+  wdm (>= 0.1.0)
 
 BUNDLED WITH
    1.11.2

activesupport/test/file_update_checker_shared_tests.rb

@@ -9,7 +9,7 @@ def tmpdir
   end
 
   def tmpfile(name)
-    "#{tmpdir}/#{name}"
+    File.join(tmpdir, name)
   end
 
   def tmpfiles
@@ -17,7 +17,9 @@ def tmpfiles
   end
 
   def run(*args)
-    Dir.mktmpdir(nil, __dir__) { |dir| @tmpdir = dir; super }
+    capture_exceptions do
+      Dir.mktmpdir(nil, __dir__) { |dir| @tmpdir = dir; super }
+    end
   end
 
   test 'should not execute the block if no paths are given' do
@@ -225,7 +227,7 @@ def run(*args)
     assert !checker.execute_if_updated
     assert_equal 0, i
 
-    touch("#{subdir}/nested.rb")
+    touch(File.join(subdir, "nested.rb"))
 
     assert checker.execute_if_updated
     assert_equal 1, i
@@ -245,12 +247,12 @@ def run(*args)
     assert_equal 0, i
 
     # subdir does not look for Ruby files, but its parent tmpdir does.
-    touch("#{subdir}/nested.rb")
+    touch(File.join(subdir, "nested.rb"))
 
     assert checker.execute_if_updated
     assert_equal 1, i
 
-    touch("#{subdir}/nested.txt")
+    touch(File.join(subdir, "nested.txt"))
 
     assert checker.execute_if_updated
     assert_equal 2, i