Powermock unable to mock MysqlConnect

Question

The is my Mysql Class:

public class MysqlConnection {

    public Connection MysqlConnect() {
        String url = "jdbc:mysql://localhost:3306/";
        String dbName = "dashboard";
        String driver = "com.mysql.jdbc.Driver";
        String userName = "root";
        String passwd = "";
        Connection conn = null;
        try {
            Class.forName(driver);
            conn = DriverManager.getConnection(url+dbName,userName,passwd);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return conn;
    }
}

And my PowerMockito test class is like this:

@RunWith(PowerMockRunner.class)
@PowerMockIgnore("javax.management.*")
@PrepareForTest(Class.class)
public class MysqlConnectionTest {

    @Test(expected = ClassNotFoundException.class)
    public void MysqlConnectiontest() {
        PowerMockito.mockStatic(Class.class);
        try {
            when(Class.forName(Mockito.anyString())).thenThrow(new ClassNotFoundException("error message"));
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        obj.MysqlConnect();
    }
}

The Stacktrace of the error is:

java.lang.AssertionError: Expected exception: java.lang.ClassNotFoundException
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:314)
at org.junit.internal.runners.MethodRoadie$2.run(MethodRoadie.java:86)
at org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:94)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.executeTest(PowerMockJUnit44RunnerDelegateImpl.java:296)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTestInSuper(PowerMockJUnit47RunnerDelegateImpl.java:112)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTest(PowerMockJUnit47RunnerDelegateImpl.java:73)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runBeforesThenTestThenAfters(PowerMockJUnit44RunnerDelegateImpl.java:284)
at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:84)
at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:49)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.invokeTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:209)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.runMethods(PowerMockJUnit44RunnerDelegateImpl.java:148)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$1.run(PowerMockJUnit44RunnerDelegateImpl.java:122)
at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:34)
at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:44)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.run(PowerMockJUnit44RunnerDelegateImpl.java:120)
at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.run(JUnit4TestSuiteChunkerImpl.java:102)
at org.powermock.modules.junit4.common.internal.impl.AbstractCommonPowerMockRunner.run(AbstractCommonPowerMockRunner.java:53)
at org.powermock.modules.junit4.PowerMockRunner.run(PowerMockRunner.java:42)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

The program is not mocking any line of code but is executing the code from the actual MySQLConnect function instead. It is making use of the actual driver. If I remove the expected part from @Test the test succeeds. That is, no mocking is done, driver is loaded and everything.

Answer 1

You cannot mock java.lang.Class with PowerMockito or any other mocking framework which relies on runtime byte code modification. Reason for this is that those classes are already loaded when the mockito agent is manipulating (instrumenting) the classes that should be mocked.

Why don't you instead mock your MysqlConnection class? There you could spy on your MysqlConnect method and return a mocked connection instead.