Runnnig Pytest while building docker compose up - docker

Question

My projects structure looks as following.
app/
docker-compose.yml
test_some_pytest.py # this have some pytest code.
tests.Dockerfile
my tests.Dockerfile looks as following.
from python:3.4-alpine
RUN python --version
RUN pip --version
COPY . /APP
WORKDIR /APP
RUN pip install pytest
RUN ["pytest"]
and docker-compose.yml as following.
services
tests:
build:
context: .
dockerfile: tests.Dockerfile
When I run docker-compose up --build tests. the pytest also run but probably at some other place. it shows the following output.
.
.
.
Removing intermediate container 96f9a8ba43d2
---> 82c89715d4c0
Step 7/7 : RUN ["pytest"]
---> Running in c30ee497e5f5
============================= test session starts ==============================
platform linux -- Python 3.4.10, pytest-4.6.11, py-1.10.0, pluggy-0.13.1
rootdir: /python-test-calculator
collected 0 items
========================= no tests ran in 0.00 seconds =========================
The command 'pytest' returned a non-zero code: 5
ERROR: Service 'tests' failed to build : Build failed

Answer 1

If I use your tests.Dockerfile exactly as written, the following docker-compose.yaml:
version: "3"
services:
tests:
build:
context: .
dockerfile: tests.Dockerfile
And the following test_some_pytest.py:
def test_something():
assert True
It successfully runs pytest when I run docker-compose build:
$ docker-compose build
Building tests
[...]
Step 7/7 : RUN ["pytest"]
---> Running in 8d8a1f44913f
============================= test session starts ==============================
platform linux -- Python 3.4.10, pytest-4.6.11, py-1.10.0, pluggy-0.13.1
rootdir: /APP
collected 1 item
test_some_pytest.py . [100%]
=========================== 1 passed in 0.01 seconds ===========================
Removing intermediate container 8d8a1f44913f
---> 055afd5b1f8d
Successfully built 055afd5b1f8d
Successfully tagged docker_tests:latest
You can see from the above output that pytest discovered and successfully ran 1 test.