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

.travis.yml

@@ -19,3 +19,7 @@ install:
 
 script:
   - tox
+
+after_success:
+  - pip install codecov
+  - codecov -v

opentelemetry-api/src/opentelemetry/context/async_context.py

@@ -12,32 +12,34 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import typing  # pylint: disable=unused-import
-from contextvars import ContextVar
+try:
+    from contextvars import ContextVar
+except ImportError:
+    pass
+else:
+    import typing  # pylint: disable=unused-import
+    from . import base_context
 
-from . import base_context
+    class AsyncRuntimeContext(base_context.BaseRuntimeContext):
+        class Slot(base_context.BaseRuntimeContext.Slot):
+            def __init__(self, name: str, default: object):
+                # pylint: disable=super-init-not-called
+                self.name = name
+                self.contextvar = ContextVar(name)  # type: ContextVar[object]
+                self.default = base_context.wrap_callable(
+                    default
+                )  # type: typing.Callable[..., object]
 
+            def clear(self) -> None:
+                self.contextvar.set(self.default())
 
-class AsyncRuntimeContext(base_context.BaseRuntimeContext):
-    class Slot(base_context.BaseRuntimeContext.Slot):
-        def __init__(self, name: str, default: "object"):
-            # pylint: disable=super-init-not-called
-            self.name = name
-            self.contextvar = ContextVar(name)  # type: ContextVar[object]
-            self.default = base_context.wrap_callable(
-                default
-            )  # type: typing.Callable[..., object]
+            def get(self) -> object:
+                try:
+                    return self.contextvar.get()
+                except LookupError:
+                    value = self.default()
+                    self.set(value)
+                    return value
 
-        def clear(self) -> None:
-            self.contextvar.set(self.default())
-
-        def get(self) -> "object":
-            try:
-                return self.contextvar.get()
-            except LookupError:
-                value = self.default()
-                self.set(value)
-                return value
-
-        def set(self, value: "object") -> None:
-            self.contextvar.set(value)
+            def set(self, value: object) -> None:
+                self.contextvar.set(value)

pytest-cov.ini

@@ -0,0 +1,6 @@
+[pytest]
+addopts = -rs -v
+
+# We need this to make pytest "touch" every python file
+# in order to include them into the coverage report.
+python_files = *.py

pytest.ini

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

scripts/coverage.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+
+set -e
+
+function cov {
+    pytest ${1} \
+        -c pytest-cov.ini \
+        --ignore-glob=*/setup.py \
+        --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-opentracing-shim
+cov ext/opentelemetry-ext-wsgi
+cov examples/opentelemetry-example-app
+
+coverage report
+coverage xml

tox.ini

@@ -4,6 +4,11 @@ skip_missing_interpreters = True
 envlist =
     py3{4,5,6,7,8}-test-{api,sdk,example-app,ext-wsgi,ext-http-requests,ext-jaeger,opentracing-shim}
     pypy3-test-{api,sdk,example-app,ext-wsgi,ext-http-requests,ext-jaeger,opentracing-shim}
+    py3{4,5,6,7,8}-coverage
+
+    ; Coverage is temporarily disabled for pypy3 due to the pytest bug.
+    ; pypy3-coverage
+
     lint
     py37-{mypy,mypyinstalled}
     docs
@@ -14,6 +19,8 @@ python =
 
 [testenv]
 deps =
+  test: pytest
+  coverage: pytest-cov
   mypy,mypyinstalled: mypy~=0.740
 
 setenv =
@@ -44,12 +51,24 @@ commands_pre =
   jaeger: pip install {toxinidir}/ext/opentelemetry-ext-jaeger
   opentracing-shim: pip install {toxinidir}/opentelemetry-sdk {toxinidir}/ext/opentelemetry-ext-opentracing-shim
 
+; 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-opentracing-shim
+  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}/scripts/coverage.sh
 
   mypy: mypy --namespace-packages opentelemetry-api/src/opentelemetry/
 ; For test code, we don't want to enforce the full mypy strictness