Debugging java test method leads to `Debugger failed to attach` about dap-mode HOT 5 CLOSED

Debugger failed to attach: handshake failed - connection prematurally closed.

Here it is how debugging works:

1. Test is started with remote debugging set to listen on port 30000
2. dap-mode starts a loop which waits for port to be taken.
3. when the port is taken, dap-mode starts the debug adapter with launch type = attach

The error message is coming from the test connection happening at 2).

Did you try to run the test without debug? Are these the only messages in the output log? Can you try to do lsp-java-build-project before starting the test?

from dap-mode.

Running the test using dap-java-run-test-method works as expected.
Running lsp-java-build-project made no difference.
The port that the debugger binds to is 33000 and it does seem to bind correctly, so for some reason the attach tings seems to fail.

from dap-mode.

Note: The error message will appear upon timeout, or upon any interaction with the editor (key press or mouse click).

from dap-mode.

Upon further investigation, I come the conclusion that this error message is misleading, as I managed to succesfully debug a test, even though the message appears (I can't get rid of it).

from dap-mode.

I was unable to find a way to test whether particular port is taken so I am opening a testing connection to the debugged process and then I am closing it - thus this error message. I am closing the bug based on the previous comment.

from dap-mode.