improve documentation

powertools-e2e-tests/README.md

@@ -1,10 +1,13 @@
 ## End-to-end tests
 This module is internal and meant to be used for end-to-end (E2E) testing of Lambda Powertools for Java. 
 
-__Prerequisites__: an AWS account is needed as well as a local environment able to reach this account 
+__Prerequisites__: 
+- An AWS account is needed as well as a local environment able to reach this account 
 ([credentials](https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/credentials.html)).
+- [Java 11+](https://docs.aws.amazon.com/corretto/latest/corretto-11-ug/downloads-list.html)
+- [Docker](https://docs.docker.com/engine/install/)
 
-To execute the E2E tests, use the following command: `mvn clean verify -Pe2e`
+To execute the E2E tests, use the following command: `export JAVA_VERSION=11 && mvn clean verify -Pe2e`
 
 ### Under the hood
 This module leverages the following components:

powertools-e2e-tests/src/test/java/software/amazon/lambda/powertools/testutils/Infrastructure.java

@@ -33,13 +33,22 @@
 
 import java.io.File;
 import java.io.IOException;
-import java.io.InputStream;
 import java.nio.file.Path;
 import java.util.*;
 import java.util.stream.Collectors;
 
 import static java.util.Collections.singletonList;
 
+/**
+ * This class is in charge of bootstrapping the infrastructure for the tests.
+ * <br/>
+ * Tests are actually run on AWS, so we need to provision Lambda functions, DynamoDB table (for Idempotency),
+ * CloudWatch log groups, ...
+ * <br/>
+ * It uses the Cloud Development Kit (CDK) to define required resources. The CDK stack is then synthesized to retrieve
+ * the CloudFormation templates and the assets (function jars). Assets are uploaded to S3 (with the SDK `PutObjectRequest`)
+ * and the CloudFormation stack is created (with the SDK `createStack`)
+ */
 public class Infrastructure {
     private static final Logger LOG = LoggerFactory.getLogger(Infrastructure.class);
 
@@ -92,6 +101,10 @@ private Infrastructure(Builder builder) {
                 .build();
     }
 
+    /**
+     * Use the CloudFormation SDK to create the stack
+     * @return the name of the function deployed part of the stack
+     */
     public String deploy() {
         uploadAssets();
         LOG.info("Deploying '" + stackName + "' on account " + account);
@@ -111,6 +124,9 @@ public String deploy() {
         return functionName;
     }
 
+    /**
+     * Destroy the CloudFormation stack
+     */
     public void destroy() {
         LOG.info("Deleting '" + stackName + "' on account " + account);
         cfn.deleteStack(DeleteStackRequest.builder().stackName(stackName).build());
@@ -193,6 +209,10 @@ public Builder timeoutInSeconds(long timeoutInSeconds) {
         }
     }
 
+    /**
+     * Build the CDK Stack containing the required resources (Lambda function, LogGroup, DDB Table)
+     * @return the CDK stack
+     */
     private Stack createStackWithLambda() {
         Stack stack = new Stack(app, stackName);
         List<String> packagingInstruction = Arrays.asList(
@@ -261,12 +281,18 @@ private Stack createStackWithLambda() {
         return stack;
     }
 
+    /**
+     * cdk synth to retrieve the CloudFormation template and assets directory
+     */
     private void synthesize() {
         CloudAssembly synth = app.synth();
         cfnTemplate = synth.getStackByName(stack.getStackName()).getTemplate();
         cfnAssetDirectory = synth.getDirectory();
     }
 
+    /**
+     * Upload assets (mainly lambda function jars) to S3
+     */
     private void uploadAssets() {
         Map<String, Asset> assets = findAssets();
         assets.forEach((objectKey, asset) -> {
@@ -283,6 +309,10 @@ private void uploadAssets() {
         });
     }
 
+    /**
+     * Reading the cdk assets.json file to retrieve the list of assets to push to S3
+     * @return a map of assets
+     */
     private Map<String, Asset> findAssets() {
         Map<String, Asset> assets = new HashMap<>();
         try {

powertools-e2e-tests/src/test/java/software/amazon/lambda/powertools/testutils/logging/InvocationLogs.java

@@ -5,9 +5,12 @@
 import java.util.Base64;
 import java.util.stream.IntStream;
 
+/**
+ * Logs for a specific Lambda invocation
+ */
 public class InvocationLogs {
-    private String[] logs;
-    private String[] functionLogs;
+    private final String[] logs;
+    private final String[] functionLogs;
 
     public InvocationLogs(String base64Logs, String requestId) {
         String rawLogs = new String(Base64.getDecoder().decode(base64Logs), StandardCharsets.UTF_8);

powertools-e2e-tests/src/test/java/software/amazon/lambda/powertools/testutils/metrics/MetricsFetcher.java

@@ -20,6 +20,10 @@
 import java.util.concurrent.Callable;
 
 import static java.time.Duration.ofSeconds;
+
+/**
+ * Class in charge of retrieving the actual metrics of a Lambda execution on CloudWatch
+ */
 public class MetricsFetcher {
     private static final Logger LOG = LoggerFactory.getLogger(MetricsFetcher.class);
 
@@ -30,6 +34,17 @@ public class MetricsFetcher {
             .region(region)
             .build();
 
+    /**
+     * Retrieve the metric values from start to end. Different parameters are required (see {@link CloudWatchClient#getMetricData} for more info).
+     * Use a retry mechanism as metrics may not be available instantaneously after a function runs.
+     * @param start
+     * @param end
+     * @param period
+     * @param namespace
+     * @param metricName
+     * @param dimensions
+     * @return
+     */
     public List<Double> fetchMetrics(Instant start, Instant end, int period, String namespace, String metricName, Map<String, String> dimensions) {
         List<Dimension> dimensionsList = new ArrayList<>();
         if (dimensions != null)

powertools-e2e-tests/src/test/java/software/amazon/lambda/powertools/testutils/tracing/TraceFetcher.java

@@ -26,6 +26,9 @@
 
 import static java.time.Duration.ofSeconds;
 
+/**
+ * Class in charge of retrieving the actual traces of a Lambda execution on X-Ray
+ */
 public class TraceFetcher {
 
     private static final ObjectMapper MAPPER = new ObjectMapper().configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
@@ -36,6 +39,12 @@ public class TraceFetcher {
     private final String filterExpression;
     private final List<String> excludedSegments;
 
+    /**
+     * @param start beginning of the time slot to search in
+     * @param end end of the time slot to search in
+     * @param filterExpression eventual filter for the search
+     * @param excludedSegments list of segment to exclude from the search
+     */
     public TraceFetcher(Instant start, Instant end, String filterExpression, List<String> excludedSegments) {
         this.start = start;
         this.end = end;
@@ -47,6 +56,12 @@ public static Builder builder() {
         return new Builder();
     }
 
+    /**
+     * Retrieve the traces corresponding to a specific function during a specific time slot.
+     * Use a retry mechanism as traces may not be available instantaneously after a function runs.
+     *
+     * @return traces
+     */
     public Trace fetchTrace() {
         Callable<Trace> callable = () -> {
             List<String> traceIds = getTraceIds();
@@ -67,6 +82,11 @@ public Trace fetchTrace() {
         return status.getResult();
     }
 
+    /**
+     * Retrieve traces from trace ids.
+     * @param traceIds
+     * @return
+     */
     private Trace getTrace(List<String> traceIds) {
         BatchGetTracesResponse tracesResponse = xray.batchGetTraces(BatchGetTracesRequest.builder()
                 .traceIds(traceIds)
@@ -110,6 +130,10 @@ private void getNestedSubSegments(List<SubSegment> subsegments, Trace traceRes,
         });
     }
 
+    /**
+     * Use the X-Ray SDK to retrieve the trace ids corresponding to a specific function during a specific time slot
+     * @return a list of trace ids
+     */
     private List<String> getTraceIds() {
         GetTraceSummariesResponse traceSummaries = xray.getTraceSummaries(GetTraceSummariesRequest.builder()
                 .startTime(start)