Add specs; minor changes to some commands

`:tabedit` now works as an alias to `:edit` with a path and
  as an alias to `:tabnew` without.
`:tabnew` is a new command that opens a new tab with a new file if used
 without a path and works as an alias to `:tabedit` with one.
`:tabclose` now works as a proper alias to `:quit` (i.e. passes the arguments)
`:edit` now works more like before - it opens a given path in a new tab.
 It also doesn't do anything if the file was modified since the last commit,
 unless forced by using `:edit!`
`:write` works properly again and doesn't overwrite files, unless forced by
 using `:write!`
`:xit` is now called `:xit` and not just `:x`
`:substitute` now properly replaces multiple groups (`:s/(a)b(c)/X\1\2X\0`)

spec/spec-helper.coffee

@@ -0,0 +1,65 @@
+ExState = require '../lib/ex-state'
+GlobalExState = require '../lib/global-ex-state'
+
+beforeEach ->
+  atom.workspace ||= {}
+
+activateExMode = ->
+  atom.workspace.open().then ->
+    atom.commands.dispatch(atom.views.getView(atom.workspace), 'ex-mode:open')
+    keydown('escape')
+    atom.workspace.getActivePane().destroyActiveItem()
+
+
+getEditorElement = (callback) ->
+  textEditor = null
+
+  waitsForPromise ->
+    atom.workspace.open().then (e) ->
+      textEditor = e
+
+  runs ->
+    # element = document.createElement("atom-text-editor")
+    # element.setModel(textEditor)
+    # element.classList.add('vim-mode')
+    # element.exState = new ExState(element, new GlobalExState)
+    #
+    # element.addEventListener "keydown", (e) ->
+    #   atom.keymaps.handleKeyboardEvent(e)
+
+    element = atom.views.getView(textEditor)
+
+    callback(element)
+
+dispatchKeyboardEvent = (target, eventArgs...) ->
+  e = document.createEvent('KeyboardEvent')
+  e.initKeyboardEvent(eventArgs...)
+  # 0 is the default, and it's valid ASCII, but it's wrong.
+  Object.defineProperty(e, 'keyCode', get: -> undefined) if e.keyCode is 0
+  target.dispatchEvent e
+
+dispatchTextEvent = (target, eventArgs...) ->
+  e = document.createEvent('TextEvent')
+  e.initTextEvent(eventArgs...)
+  target.dispatchEvent e
+
+keydown = (key, {element, ctrl, shift, alt, meta, raw}={}) ->
+  key = "U+#{key.charCodeAt(0).toString(16)}" unless key is 'escape' or raw?
+  element ||= document.activeElement
+  eventArgs = [
+    true, # bubbles
+    true, # cancelable
+    null, # view
+    key,  # key
+    0,    # location
+    ctrl, alt, shift, meta
+  ]
+
+  canceled = not dispatchKeyboardEvent(element, 'keydown', eventArgs...)
+  dispatchKeyboardEvent(element, 'keypress', eventArgs...)
+  if not canceled
+    if dispatchTextEvent(element, 'textInput', eventArgs...)
+      element.value += key
+  dispatchKeyboardEvent(element, 'keyup', eventArgs...)
+
+module.exports = {keydown, getEditorElement, activateExMode}