after activating the virtual environment, do we have to everytime install the requirements.txt code example

Example: how to test a 3rd party python library across multiple environments

# Check if the project has tox.ini file defined
# install tox library in your environment, virutal env or notebook
pip install tox

# traverse to that project directory where tox.ini is located
# start tox app
tox

# it'll start with output of unit testing result in all python environment
# that project supports