package.json test script: reg. expression to enter deeper directories?

I have a test script at my package.json:

{
  "name": "my-project",
  ...
  "scripts": {
    ...
    "test": "npm run build && mocha --compilers ts:ts-node/register --recursive src/**/*.spec.ts"
  },
  ...
}

That should be running every test found inside the /src directory, that has the following structure:

But the src/**/*.spec.ts regular expression is running only camel.spec.ts tests, but not the other ones that are found in deeper directories (bactrian.spec.ts, domestic.spec.ts, dromedary.spec.ts).

Has anyone experienced this, or knows the correct expression I should be using?