examples for the blog article Unit Tests for Concurrent Java with VMLens (#18747)

Author: ThomasKrieger

libraries-testing-2/pom.xml

@@ -190,6 +190,12 @@
             <artifactId>javalite-common</artifactId>
             <version>${javalite.version}</version>
         </dependency>
+        <dependency>
+            <groupId>com.vmlens</groupId>
+            <artifactId>api</artifactId>
+            <version>${vmlens.version}</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>
@@ -218,6 +224,24 @@
                     </argLine>
                 </configuration>
             </plugin>
+            <plugin>
+                <groupId>com.vmlens</groupId>
+                <artifactId>vmlens-maven-plugin</artifactId>
+                <version>${vmlens.version}</version>
+                <executions>
+                    <execution>
+                        <id>test</id>
+                        <goals>
+                            <goal>test</goal>
+                        </goals>
+                    </execution>
+                </executions>
+                <configuration>
+                    <includes>
+                        <include>**/BankAccountTest.java</include>
+                    </includes>
+                </configuration>
+            </plugin>
         </plugins>
     </build>
 
@@ -238,5 +262,6 @@
         <truth.version>0.32</truth.version>
         <jgotesting.version>0.12</jgotesting.version>
         <javalite.version>1.4.13</javalite.version>
+        <vmlens.version>1.2.10</vmlens.version>
     </properties>
 </project>

libraries-testing-2/src/main/java/com/baeldung/vmlens/AtomicBankAccount.java

@@ -0,0 +1,17 @@
+package com.baeldung.vmlens;
+
+public class AtomicBankAccount {
+
+    private final Object LOCK = new Object();
+    private volatile int amount;
+
+    public int getAmount() {
+        return amount;
+    }
+
+    public void update(int delta) {
+        synchronized (LOCK) {
+            amount += delta;
+        }
+    }
+}

libraries-testing-2/src/main/java/com/baeldung/vmlens/RegularFieldBankAccount.java

@@ -0,0 +1,14 @@
+package com.baeldung.vmlens;
+
+public class RegularFieldBankAccount {
+
+    private int amount;
+
+    public int getAmount() {
+        return amount;
+    }
+
+    public void update(int delta) {
+        amount += delta;
+    }
+}

libraries-testing-2/src/main/java/com/baeldung/vmlens/VolatileFieldBankAccount.java

@@ -0,0 +1,14 @@
+package com.baeldung.vmlens;
+
+public class VolatileFieldBankAccount {
+
+    private volatile int amount;
+
+    public int getAmount() {
+        return amount;
+    }
+
+    public void update(int delta) {
+        amount += delta;
+    }
+}

libraries-testing-2/src/test/java/com/baeldung/vmlens/BankAccountTest.java

@@ -0,0 +1,63 @@
+package com.baeldung.vmlens;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.anyOf;
+
+import org.junit.jupiter.api.Test;
+
+import com.vmlens.api.AllInterleavings;
+
+/**
+ * This test tests the different implementations of a concurrent bank account class.+
+ * To see what is wrong with RegularFieldBankAccount and VolatileFieldBankAccount replace
+ * AtomicBankAccount with one of those classes.
+ *
+ */
+
+class BankAccountTest {
+
+    @Test
+    public void whenParallelUpdate_thenAmountSumOfBothUpdates() throws InterruptedException {
+        try (AllInterleavings allInterleavings = new AllInterleavings("bankAccount.updateUpdate")) {
+            while (allInterleavings.hasNext()) {
+                AtomicBankAccount bankAccount = new AtomicBankAccount();
+
+                Thread first = new Thread() {
+                    @Override
+                    public void run() {
+                        bankAccount.update(5);
+                    }
+                };
+                first.start();
+                bankAccount.update(10);
+                first.join();
+
+                int amount = bankAccount.getAmount();
+                assertThat(amount, is(15));
+            }
+        }
+    }
+
+    @Test
+    public void whenParallelUpdateAndGet_thenResultEitherAmountBeforeOrAfterUpdate() throws InterruptedException {
+        try (AllInterleavings allInterleavings = new AllInterleavings("bankAccount.updateGetAmount")) {
+            while (allInterleavings.hasNext()) {
+                AtomicBankAccount bankAccount = new AtomicBankAccount();
+
+                Thread first = new Thread() {
+                    @Override
+                    public void run() {
+                        bankAccount.update(5);
+                    }
+                };
+                first.start();
+
+                int amount = bankAccount.getAmount();
+
+                assertThat(amount, anyOf(is(0), is(5)));
+                first.join();
+            }
+        }
+    }
+}