fix: #24 correct example test and docs

Author: heitorlessa

Diff for: python/example/README.md

@@ -9,7 +9,9 @@ This example uses both [tracing](https://github.com/awslabs/aws-lambda-powertool
 * **Deploy**: `sam deploy --guided`
 * **Unit Tests**: We recommend proceeding with the following commands in a virtual environment
   - **Install deps**: `pip install -r hello_world/requirements.txt && pip install -r requirements-dev.txt`
-  - **Run tests with tracing disabled**: `POWERTOOLS_TRACE_DISABLED=1 python -m pytest`
+  - **Run tests with tracing disabled and namespace set**
+    - `POWERTOOLS_METRICS_NAMESPACE="Example" POWERTOOLS_TRACE_DISABLED=1 python -m pytest`
+    - Both are necessary because `app.py` initializes them in the global scope, since both Tracer and Metrics will be initialized and configured during import time. For unit tests, we could always patch and explicitly config but env vars do just fine for this example.
 
 # Example code
 

Diff for: python/example/tests/unit/test_handler.py renamed to python/example/tests/test_handler.py

@@ -5,7 +5,6 @@
 
 from hello_world import app
 
-
 @pytest.fixture()
 def apigw_event():
     """ Generates API GW Event"""
@@ -69,13 +68,24 @@ class Context:
     invoked_function_arn: str = "arn:aws:lambda:eu-west-1:298026489:function:test"
     aws_request_id: str = "5b441b59-a550-11c8-6564-f1c833cf438c"
 
-def test_lambda_handler(apigw_event, mocker):
-
-
+def test_lambda_handler(apigw_event, mocker, capsys):
     ret = app.lambda_handler(apigw_event, Context())
     data = json.loads(ret["body"])
 
+    output = capsys.readouterr()
+    output = output.out.split('\n')
+    stdout_one_string = '\t'.join(output)
+
     assert ret["statusCode"] == 200
-    assert "message" in ret["body"]
     assert data["message"] == "hello world"
-    # assert "location" in data.dict_keys()
+    assert "location" in data
+    assert "message" in ret["body"]
+    
+    # assess custom metric was flushed in stdout/logs
+    assert "SuccessfulLocations" in stdout_one_string 
+    assert "ColdStart" in stdout_one_string 
+    assert "UniqueMetricDimension" in stdout_one_string
+
+    # assess our custom middleware ran
+    assert "Logging response after Handler is called" in stdout_one_string
+    assert "Logging event before Handler is called" in stdout_one_string