Added comments to azure-pipelines.yml file

Also:
- Changed to build on macOS instead of Ubuntu
- Make sure pytest is installed

Author: Todd Leonhardt

azure-pipelines.yml

@@ -6,8 +6,12 @@
 jobs:
 
 - job: 'Test'
+
+  # Configure Build Environment to use Azure Pipelines to build tableformatter Python project using macOS
   pool:
-    vmImage: 'Ubuntu 16.04'
+    vmImage: 'macOS 10.13'  # other options 'Ubuntu 16.04', 'VS2017-Win2016'
+
+  # Run the pipeline with multiple Python versions
   strategy:
     matrix:
       Python34:
@@ -18,23 +22,32 @@ jobs:
         python.version: '3.6'
       Python37:
         python.version: '3.7'
+    # Increase the maxParallel value to simultaneously run the job for all versions in the matrix (max 10 for free open-source)
     maxParallel: 4
 
   steps:
+    # Set the UsePythonVersion task to reference the matrix variable for its Python version
   - task: UsePythonVersion@0
     inputs:
       versionSpec: '$(python.version)'
       architecture: 'x64'
 
+    # Install dependencies - install specific PyPI packages with pip
   - script: python -m pip install --upgrade pip && pip install wcwidth
     displayName: 'Install dependencies'
 
+    # TODO: Consider adding a lint test to use flake8, pylint, or black to validate code style
+
+    # Test - test with pytest, collect coverage metrics with pytest-cov, and publish these metrics to codecov.io
   - script: |
-      pytest
-    displayName: 'pytest'
+      pip install pytest pytest-cov codecov
+      py.test --cov=tableformatter --junitxml=junit/test-results.xml --cov-report=xml --cov-report=html
+      codecov
+    displayName: 'Test with pytest'
 
+    # Publish test results to the Azure DevOps server
   - task: PublishTestResults@2
     inputs:
-      testResultsFiles: '**/test-results.xml'
+      testResultsFiles: '**/test-*.xml'
       testRunTitle: 'Python $(python.version)'
     condition: succeededOrFailed()