Local testing via ParrelSync

ParrelSync is an open-source project which allows you to open multiple Unity Editor instances, all pointing to the same Unity project (using Symbolic links).

Pros

Short iteration times
Easy to debug since every client is an Editor

Cons

Requires you to have multiple Unity Editors open

How to use?

Install ParrelSync as described in their Installation Instructions
- UPM Package installation is preferred as coherence supports it out-of-the-box
- If installing via .unitypackage, you need to set CloneMode.Enabled accordingly by yourself. For example, by adding the following script to an Editor folder in your project:

// Assets/Editor/CoherenceClone.cs
// This script is only needed if you're installing ParrelSync via .unitypackage

using Coherence.Editor;

[InitializeOnLoad]
internal class CoherenceClone
{
  static CoherenceClone()
  {
    CloneMode.Enabled = ParrelSync.ClonesManager.IsClone();
  }
}

Open ParrelSync > Clones Manager. Create a new clone, and open it.
Continue development in the main Editor. Don't edit files in the clone Editors.
Make sure bake data is up-to-date before starting to test, and that the Replication Server is running with the latest schema generated by it.
Enter Play Mode on each Editor.

coherence tells apart ParrelSync clones from the main Editor, so it's easier for you to not edit assets in clones by mistake.