Running a single test imports the whole codebase

[jxrossel]

Type: Performance Issue

Behaviour

When running a test for a given module, the whole codebase is unnecessarily imported, even if no import statements are present in said module or in __init__.py files. In codebase with slow imports, this can drastically slow down the testing/debugging process. This occurs once the tests are already discovered and on each test re-run (without code change).

Steps to reproduce:

1. Create a dummy project with 2 files. One with a time.sleep(10), the other without
2. Create 2 test files, one per dummy code file. Run the test for the file without the sleep command and you will observe that the "slow import" file is also imported

See vscode_py_test.zip

Diagnostic data

Output for Python in the Output panel (View→Output, change the drop-down the upper-right of the Output panel to Python)

2026-08-11 13:28:13.013 [info] [test-by-project] Executing tests across 1 project(s), debug=false
2026-08-11 13:28:13.014 [info] [test-by-project] Executing 1 test item(s) for project: vscode_py_test (Python 3.11)
2026-08-11 13:28:13.014 [info] [test-by-project] Running 1 test(s) for project: vscode_py_test (Python 3.11)
2026-08-11 13:28:13.015 [info] [test-by-project] Setting PROJECT_ROOT_PATH=d:\Users\JRL\vscode_py_test for unittest execution
2026-08-11 13:28:13.015 [info] Running UNITTEST execution for the following test ids: tests.fast_imp_test.TestFunc.test_func
2026-08-11 13:28:13.015 [info] Attempting to use temp directory for test ids file, file name: test-ids-a624b8e10959e9bce72b.txt
2026-08-11 13:28:13.021 [info] All environment variables set for unittest execution, PYTHONPATH: "d:\\Users\\JRL\\vscode_py_test"
2026-08-11 13:28:13.023 [info] Running unittest with arguments: c:\Users\z007459\.vscode\extensions\ms-python.python-2026.4.0-win32-x64\python_files\unittestadapter\execution.py --udiscovery -v -s ./tests -p *_test.py for workspace d:\Users\JRL\vscode_py_test 

2026-08-11 13:28:23.457 [info] [test-by-project] All project executions completed

Extension version: 2026.4.0
VS Code version: Code 1.126.0 (7e7950df89d055b5a378379db9ee14290772148a, 2026-06-23T01:46:13Z)
OS version: Windows_NT x64 10.0.26100
Modes:

• Python version (& distribution if applicable, e.g. Anaconda): 3.11.9
• Type of virtual environment used (e.g. conda, venv, virtualenv, etc.): System
• Value of the python.languageServer setting: Pylance

User Settings

languageServer: "Pylance"

testing
• unittestArgs: "<placeholder>"
• unittestEnabled: true

Installed Extensions

Extension Name	Extension Id	Version
black-formatter	ms-	2026.6.0
continue	Con	2.0.0
debugpy	ms-	2026.6.0
git-graph	mhu	1.30.0
githistory	don	0.6.20
js-debug	ms-	1.117.0
js-debug-companion	ms-	1.1.3
jsts-chat-features	Typ	0.0.4
jupyter	ms-	2025.9.1
jupyter-keymap	ms-	1.1.2
jupyter-renderers	ms-	1.3.0
matlab	Gim	3.0.2
oracle-java	Ora	26.0.0
pylint	ms-	2026.6.0
python	ms-	2026.4.0
rewrap	stk	1.16.3
vscode-js-profile-table	ms-	1.0.10
vscode-jupyter-cell-tags	ms-	0.1.9
vscode-jupyter-slideshow	ms-	0.1.6
vscode-pdf	mat	0.1.11
vscode-pylance	ms-	2026.3.1
vscode-python-envs	ms-	1.36.0