diff --git a/python/ycm/test_utils.py b/python/ycm/test_utils.py
index 3eb8fc36..4f9da546 100644
--- a/python/ycm/test_utils.py
+++ b/python/ycm/test_utils.py
@@ -22,7 +22,9 @@ import re
 import sys
 
 
-BUFNR_REGEX = re.compile( r"bufnr\('(.+)', ([0-9]+)\)" )
+BUFNR_REGEX = re.compile( r"^bufnr\('(.+)', ([0-9]+)\)$" )
+BUFWINNR_REGEX = re.compile( r"^bufwinnr\(([0-9]+)\)$" )
+BWIPEOUT_REGEX = re.compile( r"^(?:silent! )bwipeout!? ([0-9]+)$" )
 
 # One-and only instance of mocked Vim object. The first 'import vim' that is
 # executed binds the vim module to the instance of MagicMock that is created,
@@ -35,6 +37,58 @@ BUFNR_REGEX = re.compile( r"bufnr\('(.+)', ([0-9]+)\)" )
 VIM_MOCK = MagicMock()
 
 
+def MockGetBufferNumber( buffer_filename ):
+  for buffer in VIM_MOCK.buffers:
+    if buffer[ 'filename' ] == buffer_filename:
+      return buffer[ 'number' ]
+  return -1
+
+
+def MockGetBufferWindowNumber( buffer_number ):
+  for buffer in VIM_MOCK.buffers:
+    if buffer[ 'number' ] == buffer_number and 'window' in buffer:
+      return buffer[ 'window' ]
+  return -1
+
+
+def MockVimEval( value ):
+  if value == "g:ycm_min_num_of_chars_for_completion":
+    return 0
+  if value == "g:ycm_path_to_python_interpreter":
+    return ''
+  if value == "tempname()":
+    return '_TEMP_FILE_'
+  if value == "&previewheight":
+    # Default value from Vim
+    return 12
+
+  match = BUFNR_REGEX.search( value )
+  if match:
+    return MockGetBufferNumber( match.group( 1 ) )
+
+  match = BUFWINNR_REGEX.search( value )
+  if match:
+    return MockGetBufferWindowNumber( int( match.group( 1 ) ) )
+
+  raise ValueError( 'Unexpected evaluation: ' + value )
+
+
+def MockWipeoutBuffer( buffer_number ):
+  buffers = VIM_MOCK.buffers
+
+  for index, buffer in enumerate( buffers ):
+    if buffer[ 'number' ] == buffer_number:
+      return buffers.pop( index )
+
+
+def MockVimCommand( command ):
+  match = BWIPEOUT_REGEX.search( command )
+  if match:
+    return MockWipeoutBuffer( int( match.group( 1 ) ) )
+
+  raise RuntimeError( 'Unexpected command: ' + command )
+
+
 def MockVimModule():
   """The 'vim' module is something that is only present when running inside the
   Vim Python interpreter, so we replace it with a MagicMock for tests. If you
@@ -57,28 +111,8 @@ def MockVimModule():
   Failure to use this approach may lead to unexpected failures in other
   tests."""
 
-  def VimEval( value ):
-    if value == "g:ycm_min_num_of_chars_for_completion":
-      return 0
-    if value == "g:ycm_path_to_python_interpreter":
-      return ''
-    if value == "tempname()":
-      return '_TEMP_FILE_'
-    if value == "&previewheight":
-      # Default value from Vim
-      return 12
-    match = BUFNR_REGEX.search( value )
-    if match:
-      filename = match.group( 1 )
-      buffers = VIM_MOCK.buffers
-      if filename in buffers and buffers[ filename ]:
-        return buffers[ filename ].pop( 0 )
-      return -1
-
-    raise ValueError( 'Unexpected evaluation: ' + value )
-
   VIM_MOCK.buffers = {}
-  VIM_MOCK.eval = MagicMock( side_effect = VimEval )
+  VIM_MOCK.eval = MagicMock( side_effect = MockVimEval )
   sys.modules[ 'vim' ] = VIM_MOCK
 
   return VIM_MOCK
diff --git a/python/ycm/tests/vimsupport_test.py b/python/ycm/tests/vimsupport_test.py
index 7f50c9be..4bfc9bb3 100644
--- a/python/ycm/tests/vimsupport_test.py
+++ b/python/ycm/tests/vimsupport_test.py
@@ -17,7 +17,7 @@
 # You should have received a copy of the GNU General Public License
 # along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
 
-from ycm.test_utils import MockVimModule
+from ycm.test_utils import MockVimModule, MockVimCommand
 MockVimModule()
 
 from ycm import vimsupport
@@ -672,24 +672,43 @@ def CheckFilename_test():
   assert_that( vimsupport.CheckFilename( __file__ ), none() )
 
 
-def BufferExistsForFilename_test():
-  buffers = {
-    os.path.realpath( 'some_filename' ): [ 1 ],
-  }
+def BufferIsVisibleForFilename_test():
+  buffers = [
+    {
+      'number': 1,
+      'filename': os.path.realpath( 'visible_filename' ),
+      'window': 1
+    },
+    {
+      'number': 2,
+      'filename': os.path.realpath( 'hidden_filename' ),
+    }
+  ]
 
-  with patch.dict( 'vim.buffers', buffers ):
-    eq_( vimsupport.BufferExistsForFilename( 'some_filename' ), True )
-    eq_( vimsupport.BufferExistsForFilename( 'another_filename' ), False )
+  with patch( 'vim.buffers', buffers ):
+    eq_( vimsupport.BufferIsVisibleForFilename( 'visible_filename' ), True )
+    eq_( vimsupport.BufferIsVisibleForFilename( 'hidden_filename' ), False )
+    eq_( vimsupport.BufferIsVisibleForFilename( 'another_filename' ), False )
 
 
-@patch( 'vim.command' )
+@patch( 'vim.command', side_effect = MockVimCommand )
 def CloseBuffersForFilename_test( vim_command ):
-  buffers = {
-    os.path.realpath( 'some_filename' ): [ 2, 5 ],
-    os.path.realpath( 'another_filename' ): [ 1 ]
-  }
+  buffers = [
+    {
+      'number': 2,
+      'filename': os.path.realpath( 'some_filename' ),
+    },
+    {
+      'number': 5,
+      'filename': os.path.realpath( 'some_filename' ),
+    },
+    {
+      'number': 1,
+      'filename': os.path.realpath( 'another_filename' )
+    }
+  ]
 
-  with patch.dict( 'vim.buffers', buffers ):
+  with patch( 'vim.buffers', buffers ):
     vimsupport.CloseBuffersForFilename( 'some_filename' )
 
   vim_command.assert_has_calls( [