Preserve original test failure status and termination signal when teardown_test() fails, and expose test failure state during teardown

[Puneetha-Ramachandra]

Description

In hardware/device end-to-end testing, when a test case (test_*) fails, for example, because the device under test crashed, disconnected, or became unresponsive, subsequent cleanup operations in teardown_test() (or teardown_class()) frequently fail when attempting to communicate with the unhealthy device.

Currently, BaseTestClass.exec_one_test in mobly/base_test.py has several issues in how teardown_test() interacts with an already-failed test:

1. self.current_test_info.record does not reflect the test failure during teardown_test():
   In exec_one_test(), self._teardown_test(test_name) is executed inside an inner finally: block before the outer except blocks catch the exception raised by test_method() and update tr_record:

   try:
     try:
       self._setup_test(test_name)
       test_method()
     ...
     finally:
       # tr_record.result and tr_record.termination_signal are still None here!
       self._teardown_test(test_name)
   except (signals.TestFailure, AssertionError) as e:
     tr_record.test_fail(e)

   Because tr_record is only populated after _teardown_test() finishes, teardown_test() implementations cannot inspect self.current_test_info.record to determine if the test has already failed (forcing users to rely on fragile workarounds like inspecting sys.exc_info() and expects.recorder.has_error).

2. mobly.expects failures are overridden as ERROR instead of FAIL if teardown_test() fails:
   At the end of exec_one_test():

   else:
     if expects.recorder.has_error and not teardown_test_failed:
       tr_record.test_fail()
     elif not teardown_test_failed:
       tr_record.test_pass()

   If test_method() records a failure via expects.expect_true(False, ...) and teardown_test() subsequently raises an exception (or records another expect failure), teardown_test_failed is True. As a result, tr_record.test_fail() is skipped and the test is marked as ERROR rather than FAIL.

3. Raising TestAbortSignal (TestAbortClass / TestAbortAll) in teardown_test() overwrites the original test failure:
   Inside the finally: block of exec_one_test():

   try:
     self._teardown_test(test_name)
   except signals.TestAbortSignal:
     raise

   If test_method() raises AssertionError / TestFailure (or another exception) and teardown_test() detects that the device is dead and raises TestAbortClass or TestAbortAll, re-raising TestAbortSignal inside finally: replaces the active exception from test_method(). The outer except signals.TestAbortSignal as e: then records the teardown abort signal as tr_record.termination_signal, masking the root-cause failure from test_method().

Steps to Reproduce

from mobly import asserts
from mobly import base_test
from mobly import expects
from mobly import signals
from mobly import test_runner


class TeardownOverrideTest(base_test.BaseTestClass):

  def teardown_test(self):
    # Note: self.current_test_info.record.result is None here even if the test failed.
    # If teardown detects a broken device and aborts the class, or fails after an `expect`:
    raise signals.TestAbortClass("Device unreachable during teardown_test")

  def test_assertion_failure_masked_by_teardown_abort(self):
    asserts.assert_true(False, "Root cause: test assertion failed")

  def test_expect_failure_overridden_by_teardown_error(self):
    expects.expect_true(False, "Root cause: soft expectation failed")


if __name__ == "__main__":
  test_runner.main()

Expected Behavior

1. Record test failure before running teardown_test():
   Catch and record the exception from setup_test() / test_method() (and any expects.recorder errors) onto tr_record before invoking self._teardown_test(test_name), so that self.current_test_info.record accurately reflects the test's status and termination_signal during teardown_test().
2. Never overwrite a test's primary failure with a teardown failure:
   • If test_method() already failed (via exception or mobly.expects), any exception or TestAbortSignal raised in teardown_test() should be recorded in tr_record.extra_errors['teardown_test'] without overwriting tr_record.termination_signal or changing a FAIL result to ERROR.
   • If teardown_test() raises TestAbortClass or TestAbortAll after test_method() already failed, the class/run should still abort, but the failed test's termination_signal should remain the original exception from test_method().