Twister doesnt not run my tests - "No testsuites found at the specific location"

[TK5090]

Hello,

I’m currently working on setting up unit tests for my Zephyr-based application, both with and without Twister. I'm targeting the native_sim board.

I was able to successfully run the tests without Twister using:

west build -b native_sim applications/tests/subsys/modbus -p always
west flash

This works as expected.

However, I’m struggling to run the same tests with Twister.

My project follows the Zephyr workspace application structure:
zephyrproject/
├── .west/
├── zephyr/
├── bootloader/
├── modules/
├── tools/
├── <vendor/private-repositories>/
└── applications/
├──── app/
├──── arch/
├──── ..
├──── tests/
├────└── subsys/
├────└── modbus/
├────└── boards/
├────└── src/
├────└── CMakeLists.txt
├────└── prj.conf
├────└── testcase.yaml

The testcase.yaml looks like this:
tests:
subsys.modbus:
tags:
- subsys
- modbus
- modbusrtu
platform_allow:
- native_sim

When I try to run Twister:
west twister -T applications -v -p native_sim

I get the following error:
TwisterRuntimeError: No testsuites found at the specified location...

What am I missing in my configuration or folder structure that prevents Twister from detecting the test suite? Is there something specific I need to adjust in the YAML, paths, or directory layout when using a workspace-style Zephyr application?

Any help would be appreciated!