Add microseconds specs for File.mtime, .atime and .ctime

Reference: jruby/jruby#4520 (comment)

Three attemps to avoid zero in these values with small sleep (if failed).

And some code refactoring.

core/file/atime_spec.rb

@@ -4,15 +4,23 @@
   before :each do
     @file = tmp('test.txt')
     touch @file
+    3.times do
+      @atime = File.atime(@file)
+      break if @atime.usec > 0
+      sleep 0.1
+    end
   end
 
   after :each do
     rm_r @file
   end
 
   it "returns the last access time for the named file as a Time object" do
-    File.atime(@file)
-    File.atime(@file).should be_kind_of(Time)
+    @atime.should be_kind_of(Time)
+  end
+
+  it "returns the last access time for the named file with microseconds" do
+    @atime.usec.should > 0
   end
 
   it "raises an Errno::ENOENT exception if the file is not found" do

core/file/ctime_spec.rb

@@ -3,15 +3,23 @@
 describe "File.ctime" do
   before :each do
     @file = __FILE__
+    3.times do
+      @ctime = File.ctime(@file)
+      break if @ctime.usec > 0
+      sleep 0.1
+    end
   end
 
   after :each do
     @file = nil
   end
 
   it "Returns the change time for the named file (the time at which directory information about the file was changed, not the file itself)." do
-    File.ctime(@file)
-    File.ctime(@file).should be_kind_of(Time)
+    @ctime.should be_kind_of(Time)
+  end
+
+  it "Returns the change time for the named file (the time at which directory information about the file was changed, not the file itself) with microseconds." do
+    @ctime.usec.should > 0
   end
 
   it "accepts an object that has a #to_path method" do

core/file/mtime_spec.rb

@@ -3,7 +3,11 @@
 describe "File.mtime" do
   before :each do
     @filename = tmp('i_exist')
-    touch(@filename) { @mtime = Time.now }
+    3.times do
+      touch(@filename) { @mtime = Time.now }
+      break if @mtime.usec > 0
+      sleep 0.1
+    end
   end
 
   after :each do
@@ -15,6 +19,10 @@
     File.mtime(@filename).should be_close(@mtime, 2.0)
   end
 
+  it "returns the modification Time of the file with microseconds" do
+    File.mtime(@filename).usec.should > 0
+  end
+
   it "raises an Errno::ENOENT exception if the file is not found" do
     lambda { File.mtime('bogus') }.should raise_error(Errno::ENOENT)
   end