Assuming I have declare a Unity asset “HMD”, which contains 2 directories, “Scripts” and “Tests”.

(This project has been uploaded to https://github.com/hpvdt/HMD-Air/blob/d74eb803f933b6a13de33f89468bc70def1126c9/Assets/HMD/Tests/PickleSuite.cs, to demonstrate the error)

Under “Scripts” I have a class called “Pickle”:

namespace HMD.Scripts.Pickle
{
    using YamlDotNet.Serialization;
    using YamlDotNet.Serialization.NamingConventions;

    public class Yaml
    {

Under “Tests” I have a testing class called “PickeSuite”:

using NUnit.Framework;

namespace HMD.Tests
{
    using Scripts.Pickle;
    using Scripts.Streaming.VCap;

    public class PickeSuite
    {
        // A Test behaves as an ordinary method
        [Test]
        public void PickeSuiteSimplePasses()
        {
...

Upon compilation, it is reported that all namespaces under Scripts cannot be found:

1>PickleSuite.cs(5,11): Error CS0246 : The type or namespace name 'Scripts' could not be found (are you missing a using directive or an assembly reference?)
1>PickleSuite.cs(6,11): Error CS0246 : The type or namespace name 'Scripts' could not be found (are you missing a using directive or an assembly reference?)

what’s the cause of this? How to make the namespace visible?

UPDATE 1: I later opened an open-sourced example to fully understand the design of Unity testing framework:

https://github.com/nowsprinting/UnityTestExamples

When the project is fully loaded in the IDE I can immediately see the difference in namespace organisation: namely, C# compiler automatically recognise the following 4 directories under an asset as source root:

• Scripts/Editor
• Scripts/Runtime
• Tests/Editor
• Tests/Runtime

In this case, all namespaces under Scripts can work properly. How to reproduce it in any project with the exact same editor & IDE?

(I can’t find any option to do the same in my IDE)