Add test coverage collecting

I believe that we should be able to see the test coverage.

These changes:

 - make tests use pytest

 - add displaying of the test coverage

 - add sending of collected coverage data to https://codecov.io

.coveragerc

@@ -0,0 +1,4 @@
+[run]
+omit =
+    */tests/*
+    */setup.py

.gitignore

@@ -25,6 +25,7 @@ venv*/
 pip-log.txt
 
 # Unit test / coverage reports
+coverage.xml
 .coverage
 .nox
 .tox

coverage.sh

@@ -0,0 +1,29 @@
+#!/bin/bash
+
+set -e
+
+function cov {
+    pytest "${1}/tests" \
+        --cov opentelemetry-api \
+        --cov opentelemetry-sdk \
+        --cov ext \
+        --cov examples \
+        --cov-append \
+        --cov-branch \
+        --cov-report=
+}
+
+
+coverage erase
+
+cov opentelemetry-api
+cov opentelemetry-sdk
+cov ext/opentelemetry-ext-http-requests
+cov ext/opentelemetry-ext-jaeger
+cov ext/opentelemetry-ext-wsgi
+cov examples/opentelemetry-example-app
+
+coverage report
+coverage xml
+
+codecov -v

pytest.ini

@@ -0,0 +1,2 @@
+[pytest]
+addopts = -rs -v

tox.ini

@@ -4,6 +4,8 @@ skip_missing_interpreters = True
 envlist =
     py3{4,5,6,7,8}-test-{api,sdk,example-app,ext-wsgi,ext-http-requests,ext-jaeger}
     pypy3-test-{api,sdk,example-app,ext-wsgi,ext-http-requests,ext-jaeger}
+    py3{4,5,6,7,8}-coverage
+    pypy3-coverage
     lint
     py37-{mypy,mypyinstalled}
     docs
@@ -14,6 +16,9 @@ python =
 
 [testenv]
 deps =
+  test: pytest
+  coverage: pytest-cov
+  coverage: codecov
   mypy,mypyinstalled: mypy~=0.711
 
 setenv =
@@ -42,12 +47,23 @@ commands_pre =
   jaeger: pip install {toxinidir}/opentelemetry-sdk
   jaeger: pip install {toxinidir}/ext/opentelemetry-ext-jaeger
 
+; In order to get a healthy coverage report,
+; we have to install packages in editable mode.
+  coverage: pip install -e {toxinidir}/opentelemetry-api
+  coverage: pip install -e {toxinidir}/opentelemetry-sdk
+  coverage: pip install -e {toxinidir}/ext/opentelemetry-ext-azure-monitor
+  coverage: pip install -e {toxinidir}/ext/opentelemetry-ext-http-requests
+  coverage: pip install -e {toxinidir}/ext/opentelemetry-ext-jaeger
+  coverage: pip install -e {toxinidir}/ext/opentelemetry-ext-wsgi
+  coverage: pip install -e {toxinidir}/examples/opentelemetry-example-app
+
 ; Using file:// here because otherwise tox invokes just "pip install
 ; opentelemetry-api", leading to an error
   mypyinstalled: pip install file://{toxinidir}/opentelemetry-api/
 
 commands =
-  test: python -m unittest discover
+  test: pytest
+  coverage: {toxinidir}/coverage.sh
 
   mypy: mypy --namespace-packages opentelemetry-api/src/opentelemetry/
 ; For test code, we don't want to enforce the full mypy strictness