Allow metadata to be passed to atom.assert

src/atom-environment.coffee

@@ -821,12 +821,17 @@ class AtomEnvironment extends Model
   Section: Private
   ###
 
-  assert: (condition, message, callback) ->
+  assert: (condition, message, callbackOrMetadata) ->
     return true if condition
 
     error = new Error("Assertion failed: #{message}")
     Error.captureStackTrace(error, @assert)
-    callback?(error)
+
+    if callbackOrMetadata?
+      if typeof callbackOrMetadata is 'function'
+        callbackOrMetadata?(error)
+      else
+        error.metadata = callbackOrMetadata
 
     @emitter.emit 'did-fail-assertion', error