diff --git a/autoload/youcompleteme.vim b/autoload/youcompleteme.vim
index 52d9f5af..5a69051d 100644
--- a/autoload/youcompleteme.vim
+++ b/autoload/youcompleteme.vim
@@ -91,7 +91,7 @@ function! youcompleteme#Enable()
     autocmd BufReadPre * call s:OnBufferReadPre( expand( '<afile>:p' ) )
     autocmd BufRead,FileType * call s:OnBufferRead()
     autocmd BufEnter * call s:OnBufferEnter()
-    autocmd BufUnload * call s:OnBufferUnload( expand( '<afile>:p' ) )
+    autocmd BufUnload * call s:OnBufferUnload()
     autocmd CursorHold,CursorHoldI * call s:OnCursorHold()
     autocmd InsertLeave * call s:OnInsertLeave()
     autocmd InsertEnter * call s:OnInsertEnter()
@@ -323,10 +323,12 @@ function! s:TurnOffSyntasticForCFamily()
 endfunction
 
 
-function! s:AllowedToCompleteInCurrentBuffer()
-  if empty( &filetype ) ||
-        \ getbufvar( winbufnr( winnr() ), "&buftype" ) ==# 'nofile' ||
-        \ &filetype ==# 'qf'
+function! s:AllowedToCompleteInBuffer( buffer )
+  let buffer_filetype = getbufvar( a:buffer, '&filetype' )
+
+  if empty( buffer_filetype ) ||
+   \ getbufvar( a:buffer, '&buftype' ) ==# 'nofile' ||
+   \ buffer_filetype ==# 'qf'
     return 0
   endif
 
@@ -335,13 +337,18 @@ function! s:AllowedToCompleteInCurrentBuffer()
   endif
 
   let whitelist_allows = has_key( g:ycm_filetype_whitelist, '*' ) ||
-        \ has_key( g:ycm_filetype_whitelist, &filetype )
-  let blacklist_allows = !has_key( g:ycm_filetype_blacklist, &filetype )
+        \ has_key( g:ycm_filetype_whitelist, buffer_filetype )
+  let blacklist_allows = !has_key( g:ycm_filetype_blacklist, buffer_filetype )
 
   return whitelist_allows && blacklist_allows
 endfunction
 
 
+function! s:AllowedToCompleteInCurrentBuffer()
+  return s:AllowedToCompleteInBuffer( '%' )
+endfunction
+
+
 function! s:VisitedBufferRequiresReparse()
   if !s:AllowedToCompleteInCurrentBuffer()
     return 0
@@ -471,13 +478,16 @@ function! s:OnBufferEnter()
 endfunction
 
 
-function! s:OnBufferUnload( deleted_buffer_file )
-  if !s:AllowedToCompleteInCurrentBuffer() || empty( a:deleted_buffer_file )
+function! s:OnBufferUnload()
+  " Expanding <abuf> returns the unloaded buffer number as a string but we want
+  " it as a true number for the getbufvar function.
+  if !s:AllowedToCompleteInBuffer( str2nr( expand( '<abuf>' ) ) )
     return
   endif
 
+  let deleted_buffer_file = expand( '<afile>:p' )
   exec s:python_command "ycm_state.OnBufferUnload("
-        \ "vim.eval( 'a:deleted_buffer_file' ) )"
+        \ "vim.eval( 'deleted_buffer_file' ) )"
 endfunction
 
 
diff --git a/python/ycm/client/base_request.py b/python/ycm/client/base_request.py
index 97f4bf31..1fae1ea8 100644
--- a/python/ycm/client/base_request.py
+++ b/python/ycm/client/base_request.py
@@ -154,20 +154,29 @@ class BaseRequest( object ):
   hmac_secret = ''
 
 
-def BuildRequestData( include_buffer_data = True ):
+def BuildRequestData( filepath = None ):
+  """Build request for the current buffer or the buffer corresponding to
+  |filepath| if specified."""
+  current_filepath = vimsupport.GetCurrentBufferFilepath()
+
+  if filepath and current_filepath != filepath:
+    # Cursor position is irrelevant when filepath is not the current buffer.
+    return {
+      'filepath': filepath,
+      'line_num': 1,
+      'column_num': 1,
+      'file_data': vimsupport.GetUnsavedAndSpecifiedBufferData( filepath )
+    }
+
   line, column = vimsupport.CurrentLineAndColumn()
-  filepath = vimsupport.GetCurrentBufferFilepath()
-  request_data = {
+
+  return {
+    'filepath': current_filepath,
     'line_num': line + 1,
     'column_num': column + 1,
-    'filepath': filepath
+    'file_data': vimsupport.GetUnsavedAndSpecifiedBufferData( current_filepath )
   }
 
-  if include_buffer_data:
-    request_data[ 'file_data' ] = vimsupport.GetUnsavedAndCurrentBufferData()
-
-  return request_data
-
 
 def JsonFromFuture( future ):
   response = future.result()
diff --git a/python/ycm/client/event_notification.py b/python/ycm/client/event_notification.py
index b9a60d18..bd73f31f 100644
--- a/python/ycm/client/event_notification.py
+++ b/python/ycm/client/event_notification.py
@@ -32,15 +32,16 @@ from ycm.client.base_request import ( BaseRequest, BuildRequestData,
 
 
 class EventNotification( BaseRequest ):
-  def __init__( self, event_name, extra_data = None ):
+  def __init__( self, event_name, filepath = None, extra_data = None ):
     super( EventNotification, self ).__init__()
     self._event_name = event_name
+    self._filepath = filepath
     self._extra_data = extra_data
     self._cached_response = None
 
 
   def Start( self ):
-    request_data = BuildRequestData()
+    request_data = BuildRequestData( self._filepath )
     if self._extra_data:
       request_data.update( self._extra_data )
     request_data[ 'event_name' ] = self._event_name
@@ -74,8 +75,10 @@ class EventNotification( BaseRequest ):
     return self._cached_response if self._cached_response else []
 
 
-def SendEventNotificationAsync( event_name, extra_data = None ):
-  event = EventNotification( event_name, extra_data )
+def SendEventNotificationAsync( event_name,
+                                filepath = None,
+                                extra_data = None ):
+  event = EventNotification( event_name, filepath, extra_data )
   event.Start()
 
 
diff --git a/python/ycm/test_utils.py b/python/ycm/test_utils.py
index ea341684..4cee2fe4 100644
--- a/python/ycm/test_utils.py
+++ b/python/ycm/test_utils.py
@@ -33,9 +33,12 @@ import functools
 from ycmd.utils import ToUnicode
 
 
-BUFNR_REGEX = re.compile( r"^bufnr\('(.+)', ([0-9]+)\)$" )
-BUFWINNR_REGEX = re.compile( r"^bufwinnr\(([0-9]+)\)$" )
-BWIPEOUT_REGEX = re.compile( r"^(?:silent! )bwipeout!? ([0-9]+)$" )
+BUFNR_REGEX = re.compile( '^bufnr\(\'(?P<buffer_filename>.+)\', ([01])\)$' )
+BUFWINNR_REGEX = re.compile( '^bufwinnr\((?P<buffer_number>[0-9]+)\)$' )
+BWIPEOUT_REGEX = re.compile(
+  '^(?:silent! )bwipeout!? (?P<buffer_number>[0-9]+)$' )
+GETBUFVAR_REGEX = re.compile(
+  '^getbufvar\((?P<buffer_number>[0-9]+), "&(?P<option>.+)"\)$' )
 
 # 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,
@@ -49,46 +52,74 @@ VIM_MOCK = MagicMock()
 
 
 def MockGetBufferNumber( buffer_filename ):
-  for buffer in VIM_MOCK.buffers:
-    if buffer[ 'filename' ] == buffer_filename:
-      return buffer[ 'number' ]
+  for vim_buffer in VIM_MOCK.buffers:
+    if vim_buffer.name == buffer_filename:
+      return vim_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' ]
+  for vim_buffer in VIM_MOCK.buffers:
+    if vim_buffer.number == buffer_number and vim_buffer.window:
+      return vim_buffer.window
   return -1
 
 
+def MockGetBufferVariable( buffer_number, option ):
+  for vim_buffer in VIM_MOCK.buffers:
+    if vim_buffer.number == buffer_number:
+      if option == 'mod':
+        return vim_buffer.modified
+      if option == 'ft':
+        return vim_buffer.filetype
+      return ''
+  return ''
+
+
 def MockVimEval( value ):
-  if value == "g:ycm_min_num_of_chars_for_completion":
+  if value == 'g:ycm_min_num_of_chars_for_completion':
     return 0
-  if value == "g:ycm_server_python_interpreter":
+
+  if value == 'g:ycm_server_python_interpreter':
     return ''
-  if value == "tempname()":
+
+  if value == 'tempname()':
     return '_TEMP_FILE_'
-  if value == "&previewheight":
+
+  if value == '&previewheight':
     # Default value from Vim
     return 12
 
+  if value == '&omnifunc':
+    return VIM_MOCK.current.buffer.omnifunc
+
+  if value == '&filetype':
+    return VIM_MOCK.current.buffer.filetype
+
   match = BUFNR_REGEX.search( value )
   if match:
-    return MockGetBufferNumber( match.group( 1 ) )
+    buffer_filename = match.group( 'buffer_filename' )
+    return MockGetBufferNumber( buffer_filename )
 
   match = BUFWINNR_REGEX.search( value )
   if match:
-    return MockGetBufferWindowNumber( int( match.group( 1 ) ) )
+    buffer_number = int( match.group( 'buffer_number' ) )
+    return MockGetBufferWindowNumber( buffer_number )
 
-  raise ValueError( 'Unexpected evaluation: ' + value )
+  match = GETBUFVAR_REGEX.search( value )
+  if match:
+    buffer_number = int( match.group( 'buffer_number' ) )
+    option = match.group( 'option' )
+    return MockGetBufferVariable( buffer_number, option )
+
+  raise ValueError( 'Unexpected evaluation: {0}'.format( value ) )
 
 
 def MockWipeoutBuffer( buffer_number ):
   buffers = VIM_MOCK.buffers
 
   for index, buffer in enumerate( buffers ):
-    if buffer[ 'number' ] == buffer_number:
+    if buffer.number == buffer_number:
       return buffers.pop( index )
 
 
@@ -100,6 +131,50 @@ def MockVimCommand( command ):
   raise RuntimeError( 'Unexpected command: ' + command )
 
 
+class VimBuffer( object ):
+  """An object that looks like a vim.buffer object:
+   - |name|    : full path of the buffer;
+   - |number|  : buffer number;
+   - |contents|: list of lines representing the buffer contents;
+   - |filetype|: buffer filetype. Empty string if no filetype is set;
+   - |modified|: True if the buffer has unsaved changes, False otherwise;
+   - |window|  : number of the buffer window. None if the buffer is hidden;
+   - |omnifunc|: omni completion function used by the buffer."""
+
+  def __init__( self, name,
+                      number = 1,
+                      contents = [],
+                      filetype = '',
+                      modified = True,
+                      window = None,
+                      omnifunc = '' ):
+    self.name = name
+    self.number = number
+    self.contents = contents
+    self.filetype = filetype
+    self.modified = modified
+    self.window = window
+    self.omnifunc = omnifunc
+
+
+  def __getitem__( self, index ):
+    """Return the bytes for a given line at index |index|."""
+    return self.contents[ index ]
+
+
+  def __len__( self ):
+    return len( self.contents )
+
+
+  def __setitem__( self, key, value ):
+    return self.contents.__setitem__( key, value )
+
+
+  def GetLines( self ):
+    """Return the contents of the buffer as a list of unicode strings."""
+    return [ ToUnicode( x ) for x in self.contents ]
+
+
 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
diff --git a/python/ycm/tests/event_notification_test.py b/python/ycm/tests/event_notification_test.py
index 162fc77e..863631d2 100644
--- a/python/ycm/tests/event_notification_test.py
+++ b/python/ycm/tests/event_notification_test.py
@@ -23,7 +23,7 @@ from future import standard_library
 standard_library.install_aliases()
 from builtins import *  # noqa
 
-from ycm.test_utils import MockVimModule, ExtendedMock
+from ycm.test_utils import ExtendedMock, MockVimModule, VimBuffer
 MockVimModule()
 
 import contextlib
@@ -33,6 +33,7 @@ from ycm.tests.server_test import Server_test
 from ycmd.responses import ( BuildDiagnosticData, Diagnostic, Location, Range,
                              UnknownExtraConf, ServerError )
 
+from hamcrest import assert_that, contains, has_entries
 from mock import call, MagicMock, patch
 from nose.tools import eq_, ok_
 
@@ -59,46 +60,19 @@ def MockArbitraryBuffer( filetype, native_available = True ):
   """Used via the with statement, set up mocked versions of the vim module such
   that a single buffer is open with an arbitrary name and arbirary contents. Its
   filetype is set to the supplied filetype"""
-  with patch( 'vim.current' ) as vim_current:
-    def VimEval( value ):
-      """Local mock of the vim.eval() function, used to ensure we get the
-      correct behvaiour"""
 
-      if value == '&omnifunc':
-        # The omnicompleter is not required here
-        return ''
+  # Arbitrary, but valid, single buffer open.
+  current_buffer = VimBuffer( os.path.realpath( 'TEST_BUFFER' ),
+                              window = 1,
+                              filetype = filetype )
 
-      if value == 'getbufvar(0, "&mod")':
-        # Ensure that we actually send the even to the server
-        return 1
-
-      if value == 'getbufvar(0, "&ft")' or value == '&filetype':
-        return filetype
-
-      if value.startswith( 'bufnr(' ):
-        return 0
-
-      if value.startswith( 'bufwinnr(' ):
-        return 0
-
-      raise ValueError( 'Unexpected evaluation' )
-
-    # Arbitrary, but valid, cursor position
-    vim_current.window.cursor = ( 1, 2 )
-
-    # Arbitrary, but valid, single buffer open
-    current_buffer = MagicMock()
-    current_buffer.number = 0
-    current_buffer.filename = os.path.realpath( 'TEST_BUFFER' )
-    current_buffer.name = 'TEST_BUFFER'
-    current_buffer.window = 0
-
-    # The rest just mock up the Vim module so that our single arbitrary buffer
-    # makes sense to vimsupport module.
-    with patch( 'vim.buffers', [ current_buffer ] ):
-      with patch( 'vim.current.buffer', current_buffer ):
-        with patch( 'vim.eval', side_effect=VimEval ):
-          yield
+  # The rest just mock up the Vim module so that our single arbitrary buffer
+  # makes sense to vimsupport module.
+  with patch( 'vim.buffers', [ current_buffer ] ):
+    with patch( 'vim.current.buffer', current_buffer ):
+      # Arbitrary but valid cursor position.
+      with patch( 'vim.current.window.cursor', ( 1, 2 ) ):
+        yield
 
 
 @contextlib.contextmanager
@@ -310,7 +284,7 @@ class EventNotification_test( Server_test ):
         ok_( self._server_state.FileParseRequestReady() )
         self._server_state.HandleFileParseRequest()
         vim_command.assert_has_calls( [
-          PlaceSign_Call( 1, 1, 0, True )
+          PlaceSign_Call( 1, 1, 1, True )
         ] )
         eq_( self._server_state.GetErrorCount(), 1 )
         eq_( self._server_state.GetWarningCount(), 0 )
@@ -343,8 +317,8 @@ class EventNotification_test( Server_test ):
         ok_( self._server_state.FileParseRequestReady() )
         self._server_state.HandleFileParseRequest()
         vim_command.assert_has_calls( [
-          PlaceSign_Call( 2, 2, 0, False ),
-          UnplaceSign_Call( 1, 0 )
+          PlaceSign_Call( 2, 2, 1, False ),
+          UnplaceSign_Call( 1, 1 )
         ] )
         eq_( self._server_state.GetErrorCount(), 0 )
         eq_( self._server_state.GetWarningCount(), 1 )
@@ -369,7 +343,114 @@ class EventNotification_test( Server_test ):
         self._server_state.OnFileReadyToParse()
         self._server_state.HandleFileParseRequest()
         vim_command.assert_has_calls( [
-          UnplaceSign_Call( 2, 0 )
+          UnplaceSign_Call( 2, 1 )
         ] )
         eq_( self._server_state.GetErrorCount(), 0 )
         eq_( self._server_state.GetWarningCount(), 0 )
+
+
+  @patch( 'ycm.youcompleteme.YouCompleteMe._AddUltiSnipsDataIfNeeded' )
+  @patch( 'ycm.client.base_request.BaseRequest.PostDataToHandlerAsync',
+          new_callable = ExtendedMock )
+  def BufferVisit_BuildRequestForCurrentAndUnsavedBuffers_test(
+      self, post_data_to_handler_async, *args ):
+
+    current_buffer_file = os.path.realpath( 'current_buffer' )
+    current_buffer = VimBuffer( name = current_buffer_file,
+                                number = 1,
+                                contents = [ 'current_buffer_content' ],
+                                filetype = 'some_filetype',
+                                modified = False )
+
+    modified_buffer_file = os.path.realpath( 'modified_buffer' )
+    modified_buffer = VimBuffer( name = modified_buffer_file,
+                                 number = 2,
+                                 contents = [ 'modified_buffer_content' ],
+                                 filetype = 'some_filetype',
+                                 modified = True )
+
+    unmodified_buffer_file = os.path.realpath( 'unmodified_buffer' )
+    unmodified_buffer = VimBuffer( name = unmodified_buffer_file,
+                                   number = 3,
+                                   contents = [ 'unmodified_buffer_content' ],
+                                   filetype = 'some_filetype',
+                                   modified = False )
+
+    with patch( 'vim.buffers', [ current_buffer,
+                                 modified_buffer,
+                                 unmodified_buffer ] ):
+      with patch( 'vim.current.buffer', current_buffer ):
+        with patch( 'vim.current.window.cursor', ( 3, 5 ) ):
+          self._server_state.OnBufferVisit()
+
+    assert_that(
+      # Positional arguments passed to PostDataToHandlerAsync.
+      post_data_to_handler_async.call_args[ 0 ],
+      contains(
+        has_entries( {
+          'filepath': current_buffer_file,
+          'line_num': 3,
+          'column_num': 6,
+          'file_data': has_entries( {
+            current_buffer_file: has_entries( {
+              'contents': 'current_buffer_content\n',
+              'filetypes': [ 'some_filetype' ]
+            } ),
+            modified_buffer_file: has_entries( {
+              'contents': 'modified_buffer_content\n',
+              'filetypes': [ 'some_filetype' ]
+            } )
+          } ),
+          'event_name': 'BufferVisit'
+        } ),
+        'event_notification'
+      )
+    )
+
+
+  @patch( 'ycm.client.base_request.BaseRequest.PostDataToHandlerAsync',
+          new_callable = ExtendedMock )
+  def BufferUnload_BuildRequestForDeletedAndUnsavedBuffers_test(
+      self, post_data_to_handler_async ):
+
+    current_buffer_file = os.path.realpath( 'current_buffer' )
+    current_buffer = VimBuffer( name = current_buffer_file,
+                                number = 1,
+                                contents = [ 'current_buffer_content' ],
+                                filetype = 'some_filetype',
+                                modified = True )
+
+    deleted_buffer_file = os.path.realpath( 'deleted_buffer' )
+    deleted_buffer = VimBuffer( name = deleted_buffer_file,
+                                number = 2,
+                                contents = [ 'deleted_buffer_content' ],
+                                filetype = 'some_filetype',
+                                modified = False )
+
+    with patch( 'vim.buffers', [ current_buffer, deleted_buffer ] ):
+      with patch( 'vim.current.buffer', current_buffer ):
+        self._server_state.OnBufferUnload( deleted_buffer_file )
+
+    assert_that(
+      # Positional arguments passed to PostDataToHandlerAsync.
+      post_data_to_handler_async.call_args[ 0 ],
+      contains(
+        has_entries( {
+          'filepath': deleted_buffer_file,
+          'line_num': 1,
+          'column_num': 1,
+          'file_data': has_entries( {
+            current_buffer_file: has_entries( {
+              'contents': 'current_buffer_content\n',
+              'filetypes': [ 'some_filetype' ]
+            } ),
+            deleted_buffer_file: has_entries( {
+              'contents': 'deleted_buffer_content\n',
+              'filetypes': [ 'some_filetype' ]
+            } )
+          } ),
+          'event_name': 'BufferUnload'
+        } ),
+        'event_notification'
+      )
+    )
diff --git a/python/ycm/tests/vimsupport_test.py b/python/ycm/tests/vimsupport_test.py
index 785a948a..5a3127ee 100644
--- a/python/ycm/tests/vimsupport_test.py
+++ b/python/ycm/tests/vimsupport_test.py
@@ -25,14 +25,15 @@ from future import standard_library
 standard_library.install_aliases()
 from builtins import *  # noqa
 
-from ycm.test_utils import ExtendedMock, MockVimModule, MockVimCommand
+from ycm.test_utils import ( ExtendedMock, MockVimCommand, VimBuffer,
+                             MockVimModule )
 MockVimModule()
 
 from ycm import vimsupport
 from nose.tools import eq_
 from hamcrest import assert_that, calling, raises, none, has_entry
 from mock import MagicMock, call, patch
-from ycmd.utils import ToBytes, ToUnicode
+from ycmd.utils import ToBytes
 import os
 import json
 
@@ -705,34 +706,6 @@ def ReplaceChunksInBuffer_UnsortedChunks_test():
   AssertBuffersAreEqualAsBytes( expected_buffer, result_buffer )
 
 
-class MockBuffer( object ):
-  """An object that looks like a vim.buffer object, enough for ReplaceChunk to
-  generate a location list"""
-
-  def __init__( self, lines, name, number ):
-    self.lines = lines
-    self.name = name
-    self.number = number
-
-
-  def __getitem__( self, index ):
-    """ Return the bytes for a given line at index |index| """
-    return self.lines[ index ]
-
-
-  def __len__( self ):
-    return len( self.lines )
-
-
-  def __setitem__( self, key, value ):
-    return self.lines.__setitem__( key, value )
-
-
-  def GetLines( self ):
-    """ Return the contents of the buffer as a list of unicode strings"""
-    return [ ToUnicode( x ) for x in self.lines ]
-
-
 @patch( 'ycm.vimsupport.VariableExists', return_value = False )
 @patch( 'ycm.vimsupport.SetFittingHeightForCurrentWindow' )
 @patch( 'ycm.vimsupport.GetBufferNumberForFilename',
@@ -758,11 +731,14 @@ def ReplaceChunks_SingleFile_Open_test( vim_command,
     _BuildChunk( 1, 1, 2, 1, 'replacement', 'single_file' )
   ]
 
-  result_buffer = MockBuffer( [
-    'line1',
-    'line2',
-    'line3',
-  ], 'single_file', 1 )
+  result_buffer = VimBuffer(
+    'single_file',
+    contents = [
+      'line1',
+      'line2',
+      'line3'
+    ]
+  )
 
   with patch( 'vim.buffers', [ None, result_buffer, None ] ):
     vimsupport.ReplaceChunks( chunks )
@@ -845,11 +821,14 @@ def ReplaceChunks_SingleFile_NotOpen_test( vim_command,
     _BuildChunk( 1, 1, 2, 1, 'replacement', 'single_file' )
   ]
 
-  result_buffer = MockBuffer( [
-    'line1',
-    'line2',
-    'line3',
-  ], 'single_file', 1 )
+  result_buffer = VimBuffer(
+    'single_file',
+    contents = [
+      'line1',
+      'line2',
+      'line3'
+    ]
+  )
 
   with patch( 'vim.buffers', [ None, result_buffer, None ] ):
     vimsupport.ReplaceChunks( chunks )
@@ -954,11 +933,14 @@ def ReplaceChunks_User_Declines_To_Open_File_test(
     _BuildChunk( 1, 1, 2, 1, 'replacement', 'single_file' )
   ]
 
-  result_buffer = MockBuffer( [
-    'line1',
-    'line2',
-    'line3',
-  ], 'single_file', 1 )
+  result_buffer = VimBuffer(
+    'single_file',
+    contents = [
+      'line1',
+      'line2',
+      'line3'
+    ]
+  )
 
   with patch( 'vim.buffers', [ None, result_buffer, None ] ):
     vimsupport.ReplaceChunks( chunks )
@@ -1031,11 +1013,14 @@ def ReplaceChunks_User_Aborts_Opening_File_test(
     _BuildChunk( 1, 1, 2, 1, 'replacement', 'single_file' )
   ]
 
-  result_buffer = MockBuffer( [
-    'line1',
-    'line2',
-    'line3',
-  ], 'single_file', 1 )
+  result_buffer = VimBuffer(
+    'single_file',
+    contents = [
+      'line1',
+      'line2',
+      'line3'
+    ]
+  )
 
   with patch( 'vim.buffers', [ None, result_buffer, None ] ):
     assert_that( calling( vimsupport.ReplaceChunks ).with_args( chunks ),
@@ -1114,15 +1099,23 @@ def ReplaceChunks_MultiFile_Open_test( vim_command,
     _BuildChunk( 2, 1, 2, 1, 'second_file_replacement ', '2_another_file' ),
   ]
 
-  first_file = MockBuffer( [
-    'line1',
-    'line2',
-    'line3',
-  ], '1_first_file', 22 )
-  another_file = MockBuffer( [
-    'another line1',
-    'ACME line2',
-  ], '2_another_file', 19 )
+  first_file = VimBuffer(
+    '1_first_file',
+    number = 22,
+    contents = [
+      'line1',
+      'line2',
+      'line3',
+    ]
+  )
+  another_file = VimBuffer(
+    '2_another_file',
+    number = 19,
+    contents = [
+      'another line1',
+      'ACME line2',
+    ]
+  )
 
   vim_buffers = [ None ] * 23
   vim_buffers[ 22 ] = first_file
@@ -1222,9 +1215,10 @@ def _BuildChunk( start_line,
 
 @patch( 'vim.eval', new_callable = ExtendedMock )
 def AddDiagnosticSyntaxMatch_ErrorInMiddleOfLine_test( vim_eval ):
-  current_buffer = MockBuffer( [
-    'Highlight this error please'
-  ], 'some_file', 1 )
+  current_buffer = VimBuffer(
+    'some_file',
+    contents = [ 'Highlight this error please' ]
+  )
 
   with patch( 'vim.current.buffer', current_buffer ):
     vimsupport.AddDiagnosticSyntaxMatch( 1, 16, 1, 21 )
@@ -1235,9 +1229,10 @@ def AddDiagnosticSyntaxMatch_ErrorInMiddleOfLine_test( vim_eval ):
 
 @patch( 'vim.eval', new_callable = ExtendedMock )
 def AddDiagnosticSyntaxMatch_WarningAtEndOfLine_test( vim_eval ):
-  current_buffer = MockBuffer( [
-    'Highlight this warning'
-  ], 'some_file', 1 )
+  current_buffer = VimBuffer(
+    'some_file',
+    contents = [ 'Highlight this warning' ]
+  )
 
   with patch( 'vim.current.buffer', current_buffer ):
     vimsupport.AddDiagnosticSyntaxMatch( 1, 16, 1, 23, is_error = False )
@@ -1339,31 +1334,42 @@ def CheckFilename_test():
 
 
 def BufferIsVisibleForFilename_test():
-  buffers = [
-    {
-      'number': 1,
-      'filename': os.path.realpath( 'visible_filename' ),
-      'window': 1
-    },
-    {
-      'number': 2,
-      'filename': os.path.realpath( 'hidden_filename' ),
-    }
+  vim_buffers = [
+    VimBuffer(
+      os.path.realpath( 'visible_filename' ),
+      number = 1,
+      window = 1
+    ),
+    VimBuffer(
+      os.path.realpath( 'hidden_filename' ),
+      number = 2,
+      window = None
+    )
   ]
 
-  with patch( 'vim.buffers', buffers ):
+  with patch( 'vim.buffers', vim_buffers ):
     eq_( vimsupport.BufferIsVisibleForFilename( 'visible_filename' ), True )
     eq_( vimsupport.BufferIsVisibleForFilename( 'hidden_filename' ), False )
     eq_( vimsupport.BufferIsVisibleForFilename( 'another_filename' ), False )
 
 
-@patch( 'ycm.vimsupport.GetBufferNumberForFilename',
-        side_effect = [ 2, 5, -1 ] )
 @patch( 'vim.command',
         side_effect = MockVimCommand,
         new_callable = ExtendedMock )
 def CloseBuffersForFilename_test( vim_command, *args ):
-  vimsupport.CloseBuffersForFilename( 'some_filename' )
+  vim_buffers = [
+    VimBuffer(
+      os.path.realpath( 'some_filename' ),
+      number = 2
+    ),
+    VimBuffer(
+      os.path.realpath( 'some_filename' ),
+      number = 5
+    )
+  ]
+
+  with patch( 'vim.buffers', vim_buffers ):
+    vimsupport.CloseBuffersForFilename( 'some_filename' )
 
   vim_command.assert_has_exact_calls( [
     call( 'silent! bwipeout! 2' ),
@@ -1401,17 +1407,14 @@ def OpenFilename_test( vim_current, vim_command ):
   ] )
 
 
-@patch( 'ycm.vimsupport.BufferModified', side_effect = [ True ] )
-@patch( 'ycm.vimsupport.FiletypesForBuffer', side_effect = [ [ 'cpp' ] ] )
-def GetUnsavedAndCurrentBufferData_EncodedUnicodeCharsInBuffers_test( *args ):
-  mock_buffer = MagicMock()
-  mock_buffer.name = os.path.realpath( 'filename' )
-  mock_buffer.number = 1
-  mock_buffer.__iter__.return_value = [ ToBytes ( u'abc' ), ToBytes( u'fДa' ) ]
+def GetUnsavedAndSpecifiedBufferData_EncodedUnicodeCharsInBuffers_test():
+  filepath = os.path.realpath( 'filename' )
+  contents = [ ToBytes( u'abc' ), ToBytes( u'fДa' ) ]
+  vim_buffer = VimBuffer( filepath, contents = contents )
 
-  with patch( 'vim.buffers', [ mock_buffer ] ):
-    assert_that( vimsupport.GetUnsavedAndCurrentBufferData(),
-                 has_entry( mock_buffer.name,
+  with patch( 'vim.buffers', [ vim_buffer ] ):
+    assert_that( vimsupport.GetUnsavedAndSpecifiedBufferData( filepath ),
+                 has_entry( filepath,
                             has_entry( u'contents', u'abc\nfДa\n' ) ) )
 
 
diff --git a/python/ycm/vimsupport.py b/python/ycm/vimsupport.py
index 068922d4..c50641e0 100644
--- a/python/ycm/vimsupport.py
+++ b/python/ycm/vimsupport.py
@@ -116,14 +116,17 @@ def BufferModified( buffer_object ):
   return bool( int( GetBufferOption( buffer_object, 'mod' ) ) )
 
 
-def GetUnsavedAndCurrentBufferData():
+def GetUnsavedAndSpecifiedBufferData( including_filepath ):
+  """Build part of the request containing the contents and filetypes of all
+  dirty buffers as well as the buffer with filepath |including_filepath|."""
   buffers_data = {}
   for buffer_object in vim.buffers:
+    buffer_filepath = GetBufferFilepath( buffer_object )
     if not ( BufferModified( buffer_object ) or
-             buffer_object == vim.current.buffer ):
+             buffer_filepath == including_filepath ):
       continue
 
-    buffers_data[ GetBufferFilepath( buffer_object ) ] = {
+    buffers_data[ buffer_filepath ] = {
       # Add a newline to match what gets saved to disk. See #1455 for details.
       'contents': JoinLinesAsUnicode( buffer_object ) + '\n',
       'filetypes': FiletypesForBuffer( buffer_object )
diff --git a/python/ycm/youcompleteme.py b/python/ycm/youcompleteme.py
index 33a324ff..461fcb3a 100644
--- a/python/ycm/youcompleteme.py
+++ b/python/ycm/youcompleteme.py
@@ -311,16 +311,18 @@ class YouCompleteMe( object ):
     self._AddSyntaxDataIfNeeded( extra_data )
     self._AddExtraConfDataIfNeeded( extra_data )
 
-    self._latest_file_parse_request = EventNotification( 'FileReadyToParse',
-                                                          extra_data )
+    self._latest_file_parse_request = EventNotification(
+      'FileReadyToParse', extra_data = extra_data )
     self._latest_file_parse_request.Start()
 
 
   def OnBufferUnload( self, deleted_buffer_file ):
     if not self.IsServerAlive():
       return
-    SendEventNotificationAsync( 'BufferUnload',
-                                { 'unloaded_buffer': deleted_buffer_file } )
+    SendEventNotificationAsync(
+      'BufferUnload',
+      filepath = deleted_buffer_file,
+      extra_data = { 'unloaded_buffer': deleted_buffer_file } )
 
 
   def OnBufferVisit( self ):
@@ -328,7 +330,7 @@ class YouCompleteMe( object ):
       return
     extra_data = {}
     self._AddUltiSnipsDataIfNeeded( extra_data )
-    SendEventNotificationAsync( 'BufferVisit', extra_data )
+    SendEventNotificationAsync( 'BufferVisit', extra_data = extra_data )
 
 
   def OnInsertLeave( self ):