BAEL-3960 (#9070)

Bael-3960, asserting log messages with junit code.

testing-modules/testing-assertions/src/test/java/com/baeldung/junit/log/BusinessWorkerUnitTest.java

@@ -0,0 +1,48 @@
+package com.baeldung.junit.log;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.slf4j.LoggerFactory;
+
+import ch.qos.logback.classic.Level;
+import ch.qos.logback.classic.Logger;
+import ch.qos.logback.classic.LoggerContext;
+
+public class BusinessWorkerUnitTest {
+    private static MemoryAppender memoryAppender;
+    private static final String LOGGER_NAME = "com.baeldung.junit.log";
+    private static final String MSG = "This is a test message!!!";
+
+    @Before
+    public void setup() {
+        Logger logger = (Logger) LoggerFactory.getLogger(LOGGER_NAME);
+        memoryAppender = new MemoryAppender();
+        memoryAppender.setContext((LoggerContext) LoggerFactory.getILoggerFactory());
+        logger.setLevel(Level.DEBUG);
+        logger.addAppender(memoryAppender);
+        memoryAppender.start();
+
+    }
+
+    @After
+    public void cleanUp() {
+        memoryAppender.reset();
+        memoryAppender.stop();
+    }
+
+    @Test
+    public void test() {
+        BusinessWorker worker = new BusinessWorker();
+        worker.generateLogs(MSG);
+        
+        // I check that I only have 4 messages (all but trace)
+        assertThat(memoryAppender.countEventsForLogger(LOGGER_NAME)).isEqualTo(4);
+        // I look for a specific message at a specific level, and I only have 1
+        assertThat(memoryAppender.search(MSG, Level.INFO).size()).isEqualTo(1);
+        // I check that the entry that is not present is the trace level
+        assertThat(memoryAppender.contains(MSG, Level.TRACE)).isFalse();
+    }
+}

testing-modules/testing-assertions/src/test/java/com/baeldung/junit/log/MemoryAppender.java

@@ -0,0 +1,51 @@
+package com.baeldung.junit.log;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import ch.qos.logback.classic.Level;
+import ch.qos.logback.classic.spi.ILoggingEvent;
+import ch.qos.logback.core.read.ListAppender;
+
+/**
+ * In memory slf4j appender<br/>
+ * Convenient appender to be able to check slf4j invocations
+ */
+public class MemoryAppender extends ListAppender<ILoggingEvent> {
+    public void reset() {
+        this.list.clear();
+    }
+
+    public boolean contains(String string, Level level) {
+        return this.list.stream()
+          .anyMatch(event -> event.getMessage().toString().contains(string) 
+            && event.getLevel().equals(level));
+    }
+
+    public int countEventsForLogger(String loggerName) {
+        return (int) this.list.stream()
+          .filter(event -> event.getLoggerName().contains(loggerName)).count();
+    }
+
+    public List<ILoggingEvent> search(String string) {
+        return this.list.stream()
+          .filter(event -> event.getMessage().toString().contains(string))
+          .collect(Collectors.toList());
+    }
+
+    public List<ILoggingEvent> search(String string, Level level) {
+        return this.list.stream()
+          .filter(event -> event.getMessage().toString().contains(string) 
+            && event.getLevel().equals(level))
+          .collect(Collectors.toList());
+    }
+
+    public int getSize() {
+        return this.list.size();
+    }
+
+    public List<ILoggingEvent> getLoggedEvents() {
+        return Collections.unmodifiableList(this.list);
+    }
+}