Could not convert string to float: b'7.8e-' when converting the test time duration

[ader1990]

Issue description

Hello,

During one of the stestr runs from cloudbase-init on github workflows, I have seen an error (no reproduction so far) - regarding the parsing of a duration: could not convert string to float: b'7.8e-'.

Full error:

could not convert string to float: b'7.8e-'
Traceback (most recent call last):
  File "/home/runner/work/cloudbase-init-1/cloudbase-init-1/.tox/py3/lib/python3.14/site-packages/cliff/app.py", line 455, in run_subcommand
    result = cmd.run(parsed_args)
  File "/home/runner/work/cloudbase-init-1/cloudbase-init-1/.tox/py3/lib/python3.14/site-packages/cliff/command.py", line 196, in run
    return_code = self.take_action(parsed_args) or 0
                  ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^
  File "/home/runner/work/cloudbase-init-1/cloudbase-init-1/.tox/py3/lib/python3.14/site-packages/stestr/commands/run.py", line 347, in take_action
    slowest.slowest(repo_url=self.app_args.repo_url)
    ~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/cloudbase-init-1/cloudbase-init-1/.tox/py3/lib/python3.14/site-packages/stestr/commands/slowest.py", line 90, in slowest
    test_times = repo.get_test_times(repo.get_test_ids(latest_id))
  File "/home/runner/work/cloudbase-init-1/cloudbase-init-1/.tox/py3/lib/python3.14/site-packages/stestr/repository/abstract.py", line 130, in get_test_times
    known_times = self._get_test_times(test_ids)
  File "/home/runner/work/cloudbase-init-1/cloudbase-init-1/.tox/py3/lib/python3.14/site-packages/stestr/repository/file.py", line 182, in _get_test_times
    result[test_id] = float(duration)
                      ~~~~~^^^^^^^^^^
ValueError: could not convert string to float: b'7.8e-'

github actions workflow run:

https://github.com/ader1990/cloudbase-init-1/actions/runs/30522276317/job/90805156484

Expected behavior and actual behavior

To not fail.

Steps to reproduce the problem

Run stestr.

Specifications like the version of the project, operating system, or hardware

System information

• OS: Ubuntu 24.04.4
• stestr version stestr==4.2.1
• Python release (python --version):
• pip packages (pip freeze): alabaster==1.0.0,autopage==0.6.0,babel==2.18.0,certifi==2026.7.22,cffi==2.0.0,charset-normalizer==3.4.7,cliff==4.15.0,cmd2==4.0.0,coverage==7.14.3,cryptography==48.0.1,ddt==1.7.2,debtcollector==3.1.0,defusedxml==0.7.1,docutils==0.21.2,dulwich==1.2.6,fixtures==4.3.2,flake8==6.1.0,hacking==6.1.0,idna==3.18,imagesize==2.0.0,iso8601==2.1.0,Jinja2==3.1.6,markdown-it-py==4.2.0,MarkupSafe==3.0.3,mccabe==0.7.0,mdurl==0.1.2,mock==5.2.0,msgpack==1.2.1,netaddr==1.3.0,oauthlib==3.3.1,openstackdocstheme==3.6.0,oslo.config==10.5.0,oslo.context==6.5.0,oslo.i18n==6.9.0,oslo.log==8.3.0,oslo.serialization==5.11.0,oslo.utils==10.1.1,oslotest==6.1.1,packaging==26.2,pbr==7.0.3,pip==26.1.2,prettytable==3.18.0,prompt_toolkit==3.0.52,psutil==7.2.2,pycodestyle==2.11.1,pycparser==3.0,pyflakes==3.1.0,Pygments==2.20.0,pyparsing==3.3.2,pyperclip==1.11.0,pyserial==3.5,python-dateutil==2.9.0.post0,python-subunit==1.4.6,PyYAML==6.0.3,reno==4.1.0,requests==2.34.2,rfc3986==2.0.0,rich==15.0.0,rich-argparse==1.8.0,roman-numerals==4.1.0,setuptools==83.0.0,six==1.17.0,snowballstemmer==3.1.1,Sphinx==9.0.4,sphinxcontrib-applehelp==2.0.0,sphinxcontrib-devhelp==2.0.0,sphinxcontrib-htmlhelp==2.1.0,sphinxcontrib-jsmath==1.0.1,sphinxcontrib-qthelp==2.0.0,sphinxcontrib-serializinghtml==2.0.0,stestr==4.2.1,stevedore==5.9.0,testscenarios==0.6.2,testtools==2.9.1,tomlkit==0.15.0,typing_extensions==4.15.0,untangle==1.2.1,urllib3==2.7.0,voluptuous==0.16.0,wcwidth==0.8.1,wrapt==2.2.2

Additional information