你能解释一下异常在测试用例中是如何可用的吗？

Question

有一个关于在 Junits 中检查已处理异常的问题。我似乎在我的代码中做到了这一点。其他人倾向于说这是不可能的，因为该方法没有抛出异常。有人可以解释下面代码中发生的事情吗？

public class DatabaseConnector
{

private DBConnectionInfo dbObject;
private DBQueryStatements dbQueries;

void loadConnectionInfo()
{
    Properties databaseProperties = new Properties();
    try
    {
        databaseProperties.load(getClass().getClassLoader().getResourceAsStream("database.properties"));
        dbObject.setDatabaseURL(databaseProperties.getProperty("jdbc.url"));
        dbObject.setUserName(databaseProperties.getProperty("jdbc.username"));
        dbObject.setPassword(databaseProperties.getProperty("jdbc.password"));
        dbObject.setDriver(databaseProperties.getProperty("jdbc.driver"));
    } catch (IOException e)
    {

        Logger lgr = Logger.getLogger(PostgreLocationManager.class.getName());
        lgr.log(Level.SEVERE, e.getMessage(), e);
    }

}

public DBConnectionInfo connectionInit()
{

    loadConnectionInfo();

    try
    {
        Class.forName(dbObject.getDriver());
    } catch (Exception e)
    {
        Logger lgr = Logger.getLogger(PostgreLocationManager.class.getName());
        lgr.log(Level.SEVERE, e.getMessage(), e);
    }

    try
    {
        dbObject.setConnection(DriverManager.getConnection(dbObject.getDatabaseURL(), dbObject.getUserName(),
                dbObject.getPassword()));
    } catch (Exception e)
    {
        Logger lgr = Logger.getLogger(PostgreLocationManager.class.getName());
        lgr.log(Level.SEVERE, e.getMessage(), e);
    }
    return dbObject;
}
}

以上代码的测试用例。

public class DatabaseConnectorTest
{

DatabaseConnector dbConnector;
DBConnectionInfo dbModelObject;
DBQueryStatements dbQueries;

    @Before
    public void setUp() throws Exception
    {
        MockitoAnnotations.initMocks(this);
        dbModelObject = mock(DBConnectionInfo.class);
        dbQueries = mock(DBQueryStatements.class);    
        dbConnector = new DatabaseConnector(dbModelObject,dbQueries);
    }

@Test
public void testDriverFailure()
{
    when(dbModelObject.getDriver()).thenReturn("driver");
    when(dbModelObject.getDatabaseURL()).thenReturn("jdbc:postgresql://127.0.0.1:5432/testdb");
    when(dbModelObject.getUserName()).thenReturn("postgres");
    when(dbModelObject.getPassword()).thenReturn("postgres");

    try
    {
        dbConnector.connectionInit();
    } catch (Exception e)
    {
        assertTrue(e instanceof ClassNotFoundException);
    }

    verify(dbModelObject).getDriver();
}

@Test
public void testConnectionFailure()
{
    when(dbModelObject.getDriver()).thenReturn("org.postgresql.Driver");
    when(dbModelObject.getDatabaseURL()).thenReturn("jdbc:postgresql://127.0.0.1:5432/testdb");
    when(dbModelObject.getUserName()).thenReturn("uname");
    when(dbModelObject.getPassword()).thenReturn("uname");
    try
    {
        dbConnector.connectionInit();
    } catch (Exception e)
    {
        assertTrue(e instanceof SQLException);
    }

    verify(dbModelObject).getDriver();
    verify(dbModelObject).getDatabaseURL();
    verify(dbModelObject).getUserName();
    verify(dbModelObject).getPassword();
}
}

Answer 1

你可以简单地使用@Test注解

@Test(expected=RuntimeException.class)

另一种解决方案是，当您期望出现异常时，您应该让测试失败

@Test
public void testConnectionFailure()
{
    ...
    try
    {
        dbConnector.connectionInit();
        fail("an exception should be thrown...")
    } catch (Exception e)
    {
        assertTrue(e instanceof SQLException);
    }
    ...
}  

更新 #1：

我认为你的代码和测试用例不是很好，因为在你的代码中你捕获了所有“好”的异常！但他们告诉你出了什么问题。

所以让您的代码抛出这些异常。

但另一方面是：为什么要为标准 java 或 java.sql 功能（ClassLoading、DriverManager）编写测试用例？

更新 #2：

我会用你的例子来解释，因为我不是英语本地人。 ;)

您的代码：

try
{
        Class.forName(dbObject.getDriver());  
} catch (Exception e)
{
        Logger lgr = Logger.getLogger(PostgreLocationManager.class.getName());
        lgr.log(Level.SEVERE, e.getMessage(), e);
}

您的代码：

try
{
        Do something from java standard. //Class.forName(dbObject.getDriver());  
} if an exception occures, go in this block //catch (Exception e) 
{
        Just print out the exception. 
        If someone knowns about your application he'll take a look in the log. 
        If not, your exception is lost, after leaving this block.
        And I think here is your problem!
        Do not catch any exceptions in a so low level of your application.
}

你的测试用例：

@Test
public void testDriverFailure()
{
    ....
    try
    {
        dbConnector.connectionInit();
    } catch (Exception e)
    {
        assertTrue(e instanceof ClassNotFoundException);
    }
}

你的测试用例：

@Test
public void testDriverFailure()
{
    ....
    try
    {
        try to init your dbConnector. 
    } Catch exceptions (
          They never thrown, because you already catched them in the method connectionInit().
          And here right now, you know, why its a bad idea 
          to catch exceptions and place them into logfiles (except in the very high level of your application)!
      )
    {
        Now Check, that the Java-VM ClassLoader (Not your code!!!) will throw an ClassNotFoundException. 
        Why you not trusting the jvm developers? ;)
    }
}

Answer 2

您在代码中捕获异常并将某些内容写入日志。因此，测试看不到异常，您无法测试它是否被抛出。但是您可以测试您是否记录了某些内容。另一种方法是测试您的代码是否不会引发异常并返回 null。

Answer 3

connectionInit () 方法，正如它目前所写的那样，不会引发任何异常。在您的两个测试用例中，您应该检查预期的失败（根据我对您的代码的理解），但是如果没有发生失败，您不会调用 fail () JUnit 方法，所以您的印象是您的测试用例两者都通过，而他们都应该失败。正如 Mirko 所说，您应该在调用 connectionInit () 之后将代码更改为调用 fail ()。