Embedded test example

Account.java

import org.junit.Test;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;

public class Account {

    public static class InsufficientFundsException extends Exception {
    }

    private int balance;

    public synchronized void transferTo(final int amount, final Account destination) throws InsufficientFundsException {
        synchronized (destination) {
            withdraw(amount);
            destination.deposit(amount);
        }
    }

    public synchronized void withdraw(int amount) throws InsufficientFundsException {
        if (sufficientFunds(amount)) {
            balance -= amount;
        } else {
            throw new InsufficientFundsException();
        }
    }

    public synchronized void deposit(int amount) {
        balance += amount;
    }

    public synchronized int balance() {
        return balance;
    }

    private boolean sufficientFunds(int amount) {
        return balance >= amount;
    }

    @Test
    public void testTransactions() throws Account.InsufficientFundsException {
        Account account = new Account();
        account.deposit(100);
        assertEquals(100, account.balance());
        account.withdraw(60);
        assertEquals(40, account.balance());
    }

    @Test(expected = Account.InsufficientFundsException.class)
    public void testFailedTransaction() throws Account.InsufficientFundsException {
        Account account = new Account();
        account.deposit(100);
        assertEquals(100, account.balance());
        account.withdraw(101);
    }

    @Test
    public void testTransfer() throws Account.InsufficientFundsException {
        Account account1 = new Account();
        Account account2 = new Account();
        account1.deposit(100);
        account1.transferTo(100, account2);
        assertEquals(100, account2.balance());
        assertEquals(0, account1.balance());
    }

    @Test
    public void testFailedTransfer() throws Account.InsufficientFundsException {
        Account account1 = new Account();
        Account account2 = new Account();
        account1.deposit(100);
        boolean caught = false;
        try {
            account1.transferTo(101, account2);
        } catch (final Account.InsufficientFundsException ife) {
            caught = true;
        }

        assertTrue(caught);
        assertEquals(0, account2.balance());
        assertEquals(100, account1.balance());
    }

    static {
        TestUtilities.runTests(Account.class);
    }

}

TestUtilities.java

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import org.junit.Test;

public class TestUtilities {

    private TestUtilities() {
        throw new AssertionError("static utility class is not intended to be instantiated");
    }

    /**
     * Execute all of the methods in a supplied class that have a @Test annotation.
     *
     * @param c the Class to test
     * @throws AssertionError if any tests fail
     */
    public static void runTests(final Class c) {
        try {
            for (final Method method : c.getMethods()) {
                boolean isTestMethod = method.isAnnotationPresent(Test.class);
                final Object o = c.getDeclaredConstructor().newInstance();
                if (isTestMethod) {
                    final Test test = method.getDeclaredAnnotation(Test.class);
                    try {
                        method.invoke(o, null);
                    } catch (final InvocationTargetException ite) {
                        final Throwable targetException = ite.getTargetException();
                        if (!test.expected().isInstance(targetException)) {
                            throw new AssertionError(String.format("unexpected exception type thrown: %s",
                                    targetException.getClass().getName()), targetException);
                        }
                    }
                }
            }
        } catch (final Exception e) {
            throw new AssertionError(e);
        }
    }

}