Pytest generating a large number of lines at the end in travis output causing it to fail

I have a travis build on github that runs pytest. Locally everything works fine, but on travis pytest appear to be creating thousands of lines with the module names continuously repeated at the bottom after all the tests have passed. It's unclear to me what's causing this. Could it be a pytest issue? Any suggestions would be greatly appreciated.

You can see the travis output here:

This is the travis yaml file

language: python


python:
  - "3.6"

os:
  - linux

install:
  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then MINICONDA_OS=Linux; else MINICONDA_OS=MacOSX; fi
  - wget https://repo.anaconda.com/miniconda/Miniconda3-latest-$MINICONDA_OS-x86_64.sh -O miniconda.sh
  - bash miniconda.sh -b -p "$HOME"/miniconda
  - source "$HOME"/miniconda/etc/profile.d/conda.sh
  - conda config --set always_yes yes --set changeps1 no --set auto_update_conda false
  - export LANG=en_US.UTF-8
  - export COVERAGE_DIR=":$HOME/htmlcov"
  - pip install -r requirements.txt
  - printenv | sort
  - conda install gcc_linux-64 gxx_linux-64 -c anaconda

# command to run tests
script: pytest --log-cli-level=ERROR

after_success:
  - codecov

Using this pytest.ini:

[pytest]
addopts = -s
python_functions = test_*