YCM + Omnisharp test case

.vimrc

set nocompatible

execute pathogen#infect()

syntax on

omnisharp.vim

" $HOME/.vim/plugin/omnisharp.vim

"This is the default value, setting it isn't actually necessary
let g:OmniSharp_host = "http://localhost:2000"

"let g:OmniSharp_server_type = 'roslyn'

"Set the type lookup function to use the preview window instead of the status line
"let g:OmniSharp_typeLookupInPreview = 1

"Timeout in seconds to wait for a response from the server
let g:OmniSharp_timeout = 1

"Showmatch significantly slows down omnicomplete
"when the first match contains parentheses.
set noshowmatch

"Super tab settings - uncomment the next 4 lines
"let g:SuperTabDefaultCompletionType = 'context'
"let g:SuperTabContextDefaultCompletionType = "<c-x><c-o>"
"let g:SuperTabDefaultCompletionTypeDiscovery = ["&omnifunc:<c-x><c-o>","&completefunc:<c-x><c-n>"]
"let g:SuperTabClosePreviewOnPopupClose = 1

"don't autoselect first item in omnicomplete, show if only one item (for preview)
"remove preview if you don't want to see any documentation whatsoever.
set completeopt=longest,menuone,preview
" Fetch full documentation during omnicomplete requests.
" There is a performance penalty with this (especially on Mono)
" By default, only Type/Method signatures are fetched. Full documentation can still be fetched when
" you need it with the :OmniSharpDocumentation command.
" let g:omnicomplete_fetch_documentation=1

" Get Code Issues and syntax errors
let g:syntastic_cs_checkers = ['syntax', 'semantic', 'issues']
" If you are using the omnisharp-roslyn backend, use the following
" let g:syntastic_cs_checkers = ['code_checker']
augroup omnisharp_commands
    autocmd!

    "Set autocomplete function to OmniSharp (if not using YouCompleteMe completion plugin)
    autocmd FileType cs setlocal omnifunc=OmniSharp#Complete

    " Synchronous build (blocks Vim)
    "autocmd FileType cs nnoremap <F5> :wa!<cr>:OmniSharpBuild<cr>
    " Builds can also run asynchronously with vim-dispatch installed
    autocmd FileType cs nnoremap <leader>b :wa!<cr>:OmniSharpBuildAsync<cr>
    " automatic syntax check on events (TextChanged requires Vim 7.4)
"     if v:version >= 704
"         autocmd BufEnter,TextChanged,InsertLeave *.cs SyntasticCheck
"     endif

    " Automatically add new cs files to the nearest project on save
    autocmd BufWritePost *.cs call OmniSharp#AddToProject()

    "show type information automatically when the cursor stops moving
    autocmd CursorHold *.cs call OmniSharp#TypeLookupWithoutDocumentation()

    "The following commands are contextual, based on the current cursor position.

    autocmd FileType cs nnoremap gd :OmniSharpGotoDefinition<cr>
    autocmd FileType cs nnoremap <leader>fi :OmniSharpFindImplementations<cr>
    autocmd FileType cs nnoremap <leader>ft :OmniSharpFindType<cr>
    autocmd FileType cs nnoremap <leader>fs :OmniSharpFindSymbol<cr>
    autocmd FileType cs nnoremap <leader>fu :OmniSharpFindUsages<cr>
    "finds members in the current buffer
    autocmd FileType cs nnoremap <leader>fm :OmniSharpFindMembers<cr>
    " cursor can be anywhere on the line containing an issue
    autocmd FileType cs nnoremap <leader>x  :OmniSharpFixIssue<cr>
    autocmd FileType cs nnoremap <leader>fx :OmniSharpFixUsings<cr>
    autocmd FileType cs nnoremap <leader>tt :OmniSharpTypeLookup<cr>
    autocmd FileType cs nnoremap <leader>dc :OmniSharpDocumentation<cr>
    "navigate up by method/property/field
    autocmd FileType cs nnoremap <C-K> :OmniSharpNavigateUp<cr>
    "navigate down by method/property/field
    autocmd FileType cs nnoremap <C-J> :OmniSharpNavigateDown<cr>

augroup END


" Contextual code actions (requires CtrlP or unite.vim)
nnoremap <leader><space> :OmniSharpGetCodeActions<cr>
" Run code actions with text selected in visual mode to extract method
vnoremap <leader><space> :call OmniSharp#GetCodeActions('visual')<cr>

" rename with dialog
nnoremap <leader>nm :OmniSharpRename<cr>
"nnoremap <F2> :OmniSharpRename<cr>
" rename without dialog - with cursor on the symbol to rename... ':Rename newname'
command! -nargs=1 Rename :call OmniSharp#RenameTo("<args>")

" Force OmniSharp to reload the solution. Useful when switching branches etc.
nnoremap <leader>ls :OmniSharpReloadSolution<cr>
nnoremap <leader>cf :OmniSharpCodeFormat<cr>
" Load the current .cs file to the nearest project
nnoremap <leader>tp :OmniSharpAddToProject<cr>

" (Experimental - uses vim-dispatch or vimproc plugin) - Start the omnisharp server for the current solution
nnoremap <leader>ss :OmniSharpStartServer<cr>
nnoremap <leader>sp :OmniSharpStopServer<cr>

" Add syntax highlighting for types and interfaces
nnoremap <leader>th :OmniSharpHighlightTypes<cr>
"Don't ask to save when changing buffers (i.e. when jumping to a type definition)
set hidden

ycm compile --omnisharp-completer, how work with dotnet core?
You have experience in this?