created unit tests and fixed bug that failed tests

Signed-off-by: NDavid Heinemeier Hansson <david@loudthinking.com>

activesupport/lib/active_support/cache.rb

@@ -138,7 +138,7 @@ def silence!
       #   cache.fetch("foo")  # => nil
       def fetch(key, options = {})
         @logger_off = true
-        if !options[:force] && value = read(key, options)
+        if !options[:force] && ((value = read(key, options)) || exist?(key, options))
           @logger_off = false
           log("hit", key, options)
           value

activesupport/test/caching_test.rb

@@ -90,7 +90,27 @@ def test_should_read_and_write_nil
     @cache.write('foo', nil)
     assert_equal nil, @cache.read('foo')
   end
-
+  
+  def test_should_read_and_write_false
+    @cache.write('foo', false)
+    assert_equal false, @cache.read('foo')
+  end
+  
+  def test_should_read_and_write_true
+    @cache.write('foo', true)
+    assert_equal true, @cache.read('foo')
+  end
+  
+  def test_fetch_false_without_cache_miss
+    @cache.write('foo', false)
+    assert_equal false, @cache.fetch('foo') { 'baz' }
+  end
+  
+  def test_fetch_nil_without_cache_miss
+    @cache.write('foo', nil)
+    assert_equal nil, @cache.fetch('foo') { 'baz' }
+  end
+  
   def test_fetch_without_cache_miss
     @cache.write('foo', 'bar')
     assert_equal 'bar', @cache.fetch('foo') { 'baz' }