feat: add the LogTestProcessesOutputExtension for convenience

Author: netmikey

README.md

@@ -249,6 +249,23 @@ public class MyTest {
 For more examples, see the [functional tests](https://github.com/netmikey/testprocesses/tree/main/testprocesses-core/src/test/java/io/github/netmikey/testprocesses/functional) in the `testprocesses-core` module.
 
 
+### Automatically logging a process' stdOut/stdErr streams
+
+Testprocesses can automatically log the content of a test process' stdOut/stdErr streams. This can be done in 2 ways.
+
+To log the full stdOut/stdErr streams of each process when it terminates, you can set the logger `io.github.netmikey.testprocesses.TestProcessesRegistry` to the `TRACE` level. This is useful to obtain diagnostic information if a process crashes on startup.
+
+Alternatively, you can extend your test(s) with the `io.github.netmikey.testprocesses.extensions.LogTestProcessesOutputExtension` JUnit Jupiter extension. This logs only the part of each process' stdOut/stdErr streams after each test that was emitted during that test. This is useful to associate the part of a testprocess' output with the exact test that caused it.
+
+```java
+@SpringBootTest
+@ExtendWith(LogTestProcessesOutputExtension.class)
+@TestProcess(SomeTestProcessDefinition.class)
+public class MyTest {
+    // ...
+}
+```
+
 ## Limitations
 
 Because the framework tries to reuse running test processes between tests (if not told otherwise), a test process becomes a shared resource and is, by nature, quite stateful. Because of this, running tests in parallel will most probably not behave as expected.

testprocesses-core/build.gradle

@@ -14,14 +14,14 @@ dependencyManagement {
 dependencies {
     implementation("jakarta.annotation:jakarta.annotation-api")
     implementation("org.slf4j:slf4j-api")
+    implementation("org.junit.jupiter:junit-jupiter")
     implementation("org.springframework:spring-beans")
     implementation("org.springframework:spring-context")
     implementation("org.springframework:spring-core")
     implementation("org.springframework:spring-test")
     implementation("org.springframework.boot:spring-boot-autoconfigure")
 
     testImplementation("org.springframework.boot:spring-boot-starter-test")
-    testImplementation("org.junit.jupiter:junit-jupiter")
 
     testRuntimeOnly('org.junit.platform:junit-platform-launcher')
 }

testprocesses-core/src/main/java/io/github/netmikey/testprocesses/extensions/LogTestProcessesOutputExtension.java

@@ -0,0 +1,49 @@
+package io.github.netmikey.testprocesses.extensions;
+
+import org.junit.jupiter.api.extension.AfterEachCallback;
+import org.junit.jupiter.api.extension.Extension;
+import org.junit.jupiter.api.extension.ExtensionContext;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+import org.springframework.util.StringUtils;
+
+import io.github.netmikey.testprocesses.TestProcessDefinition;
+import io.github.netmikey.testprocesses.TestProcessDefinitionBy;
+import io.github.netmikey.testprocesses.TestProcessesRegistry;
+import io.github.netmikey.testprocesses.utils.StreamStart;
+
+/**
+ * A JUnit {@link Extension} that logs <code>stdOut</code> and
+ * <code>stdErr</code> streams of each currently running test process after each
+ * test. Only the output that has been produced on the stdOut/stdErr streams
+ * during the current test is logged. If no output has been produced on a
+ * stream, it is not logged.
+ */
+public class LogTestProcessesOutputExtension implements AfterEachCallback {
+
+    private static final org.slf4j.Logger LOG = org.slf4j.LoggerFactory
+        .getLogger(LogTestProcessesOutputExtension.class);
+
+    @Override
+    public void afterEach(ExtensionContext context) throws Exception {
+        TestProcessesRegistry registry = SpringExtension.getApplicationContext(context)
+            .getBean(TestProcessesRegistry.class);
+        registry.runningProcessIdentifiers().forEach(processIdentifier -> {
+            TestProcessDefinitionBy<? extends TestProcessDefinition> selector = TestProcessDefinitionBy
+                .processIdentifier(processIdentifier);
+            logStream(processIdentifier, "stdOut", registry.stdOutAsStringOf(selector, StreamStart.CURRENT_TEST));
+            logStream(processIdentifier, "stdErr", registry.stdErrAsStringOf(selector, StreamStart.CURRENT_TEST));
+        });
+    }
+
+    private void logStream(String processIdentifier, String streamName, String content) {
+        if (StringUtils.hasText(content)) {
+            String title = processIdentifier;
+            String delimiter = "-------------------- %s %s --------------------"
+                .formatted(title, streamName);
+            LOG.info("\n{}\n{}\n{}",
+                delimiter,
+                content.replaceAll("\r?\n$", "").replaceAll("(^|\r?\n)", "$1  "),
+                "-".repeat(delimiter.length()));
+        }
+    }
+}