Adds test information

Author: edumco

pipeline/tests.md

@@ -1,14 +1,83 @@
-# Tests
+# Testing with PyTest
 
-The most essencial step is the test
+To test an python app is necessary to use some test toll like nose or Pytest. Ins this example we use PyTest for simplicity.
 
-    FROM python:3.8-slim as requirements
-    COPY requirements.txt /tmp/requirements.txt
-    RUN pip install -r /tmp/requirements.txt
+## Writting the tests
 
+Pytest searches for tests based on the naming convention in the test files:
 
-    FROM requirements as unittests
-    COPY src /app
-    RUN mkdir /reports
-    WORKDIR /app
-    RUN pytest test-pass.py --junit-xml=/reports/unit.xml
+1. Test cases are functions with name starting with `test_`
+
+2. Test files should start with `test_`
+
+3. Classes with tests should end with `_Tests`
+
+All test cases should consist at least of an assertion
+
+```python
+def test_pass():
+    assert True
+```
+
+## Configuring PyTest
+
+If you want to use your own name convention or configure other properties you can do it by creating a `pytest.ini` in the root of the test folder.
+
+In this example I just configure the junit report to generate files in the old format to be used on CI-CD tools
+
+```ini
+# content of pytest.ini
+[pytest]
+junit_family=legacy
+```
+
+## Test Requirements
+
+Its a good practicie use a exclusive requiremts file for the testing because these tools should not be package together with the application.
+
+So we create a second file called requirements-test.txt in the sample aplication folder.
+
+```python
+# Pytest dependency tree for pytest==5.4.1
+attrs==19.3.0
+importlib-metadata==1.5.0
+more-itertools==8.2.0
+packaging==20.3
+pluggy==0.13.1
+py==1.8.1
+pyparsing==2.4.6
+six==1.14.0
+wcwidth==0.1.8
+zipp==3.1.0
+
+    pytest==5.4.1
+```
+
+The contents of this file are dependencies from the package `pytest` listed with the dependencies ccomming first and the dependants last.
+
+## Dockerfile layer
+
+On the Dockerfile we create a new layer reusing the requirement layer and naming it as test. Then we copy the app code and execute the tests:
+
+```Dockerfile
+FROM python:3.8-slim as requirements
+COPY requirements.txt /tmp/requirements.txt
+RUN pip install -r /tmp/requirements.txt
+
+
+FROM requirements as test
+COPY src /app
+RUN mkdir /reports
+WORKDIR /app
+RUN pytest --junit-xml=/reports/unit.xml
+```
+
+The command who execute the tests is
+
+```Dockerfile
+RUN pytest --junit-xml=/reports/unit.xml
+```
+
+It calls the pytest packaging passing the option `--junit-xml` that generate a report in the given path.
+
+The pytest command searches for python tests and find a simple test we added before.