[Fix] Add missing dependencies: opencv-python-headless and expecttest

[IonThief]

Motivation

ModuleNotFoundError encountered when installing mmengine from source or running tests in a fresh environment.

Currently, the requirements/runtime.txt file is missing opencv-python-headless, which is present in runtime_lite.txt but not linked in the full runtime requirements. This causes pip install . to create an environment where cv2 is missing.

Additionally, expecttest is required by the test suite but is missing from requirements/tests.txt.

Modification

Added opencv-python-headless to requirements/runtime.txt

Added expecttest to requirements/tests.txt

BC-breaking

No

This change only adds missing dependencies to ensure the environment is built correctly. It does not remove or change existing APIs.

Use cases

Case 1: Installing from source

User clones the repo and runs pip install .

Before: ImportError: No module named cv2

After: OpenCV is installed as part of MMEngine installation

Case 2: Running tests

User runs pytest tests

Before: Failed tests with ModuleNotFoundError: No module named expecttest

After: Tests run properly

Checklist

• Pre-commit or other linting tools are used to fix the potential lint issues.

• The modification is covered by complete unit tests. (N/A, this is a dependency fix)

• If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDetection or MMPretrain. (Safe, adds missing dependencies only)

• The documentation has been modified accordingly, like docstring or example tutorials. (N/A)

[CLAassistant]

All committers have signed the CLA.