Mocking Logger and LoggerFactory with PowerMock and Mockito

Question

I have the following Logger I want to mock out  but to validate log entries are getting called  not for the content   private static Logger logger            LoggerFactory getLogger GoodbyeController class     I want to Mock ANY class that is used for LoggerFactory getLogger   but I could not find out how to do that  This is what I ended up with so far    Before public void performBeforeEachTest         PowerMockito mockStatic LoggerFactory class       when LoggerFactory getLogger GoodbyeController class            thenReturn loggerMock        when loggerMock isDebugEnabled    thenReturn true       doNothing   when loggerMock  error any String class                 I would like to know    Can I Mock the static LoggerFactory getLogger   to work for any class  I can only seem to run when loggerMock isDebugEnabled    thenReturn true   in the  Before and thus I cannot seem to change the characteristics per method  Is there a way around this      Edit findings   I thought I tried this already and it didnt work    when LoggerFactory getLogger any Class class    thenReturn loggerMock     But thank you  as it did work   However I have tried countless variations to   when loggerMock isDebugEnabled    thenReturn true     I cannot get the loggerMock to change its behavior outside of  Before but this only happens with Coburtura  With Clover  the coverage shows 100  but there is still an issue either way   I have this simple class   public ExampleService      private static final Logger logger               LoggerFactory getLogger ExampleService class        public String getMessage                 if logger isDebugEnabled             logger debug  isDebugEnabled            logger debug  isDebugEnabled              return  Hello world                      Then I have this test    RunWith PowerMockRunner class   PrepareForTest  LoggerFactory class   public class ExampleServiceTests         Mock     private Logger loggerMock      private ExampleServiceservice   new ExampleService          Before     public void performBeforeEachTest             PowerMockito mockStatic LoggerFactory class           when LoggerFactory getLogger any Class class                 thenReturn loggerMock              PowerMockito verifyStatic       fails             Test     public void testIsDebugEnabled True   throws Exception           when loggerMock isDebugEnabled    thenReturn true           doNothing   when loggerMock  debug any String class             assertThat service getMessage    is  Hello null  0               verify loggerMock  atLeast 1   isDebugEnabled       fails             Test     public void testIsDebugEnabled False   throws Exception           when loggerMock isDebugEnabled    thenReturn false           doNothing   when loggerMock  debug any String class             assertThat service getMessage    is  Hello null  0               verify loggerMock  atLeast 1   isDebugEnabled       fails           In clover I show 100  coverage of the if logger isDebugEnabled     block  But if I try to verify the loggerMock   verify loggerMock  atLeast 1   isDebugEnabled      I get zero interactions  I also tried PowerMockito verifyStatic    in  Before but that also has zero interactions   This just seems strange that Cobertura shows the if logger isDebugEnabled     as being not 100  complete  and Clover does  but both agree the verification fails

User · Answer

In answer to your first question  it should be as simple as replacing      when LoggerFactory getLogger GoodbyeController class   thenReturn loggerMock     with     when LoggerFactory getLogger any Class class    thenReturn loggerMock     Regarding your second question  and possibly the puzzling behavior with the first   I think the problem is that logger is static   So    private static Logger logger   LoggerFactory getLogger GoodbyeController class     is executed when the class is initialized  not the when the object is instantiated   Sometimes this can be at about the same time  so you ll be OK  but it s hard to guarantee that   So you set up LoggerFactory getLogger to return your mock  but the logger variable may have already been set with a real Logger object by the time your mocks are set up   You may be able to set the logger explicitly using something like ReflectionTestUtils  I don t know if that works with static fields  or change it from a static field to an instance field   Either way  you don t need to mock LoggerFactory getLogger because you ll be directly injecting the mock Logger instance

User · Answer

I think you can reset the invocations using Mockito reset mockLog   You should call this before every test  so inside  Before would be a good place

User · Answer

The following is a test class that mocks private static final Logger named log in class LogUtil  In addition to mocking the getLogger factory call  it is necessary to explicitly set the field using reflection  in  BeforeClass public class LogUtilTest        private static Logger logger       private static MockedStatic lt LoggerFactory gt  loggerFactoryMockedStatic                  Since   link LogUtil log  being a static final variable it is only initialized once at the class load time        So assertions are also performed against the same mock   link LogUtilTest logger               BeforeClass     public static void beforeClass             logger   mock Logger class           loggerFactoryMockedStatic   mockStatic LoggerFactory class           loggerFactoryMockedStatic when    - gt  LoggerFactory getLogger anyString     thenReturn logger           Whitebox setInternalState LogUtil class   quot log quot   logger               AfterClass     public static void after             loggerFactoryMockedStatic close

User · Answer

Somewhat late to the party - I was doing something similar and needed some pointers and ended up here  Taking no credit - I took all of the code from Brice but got the  zero interactions  than Cengiz got    Using guidance from what jheriks amd Joseph Lust had put I think I know why - I had my object under test as a field and newed it up in a  Before unlike Brice  Then the actual logger was not the mock but a real class init d as jhriks suggested      I would normally do this for my object under test so as to get a fresh object for each test  When I moved the field to a local and newed it in the test it ran ok  However  if I tried a second test it was not the mock in my test but the mock from the first test and I got the zero interactions again    When I put the creation of the mock in the  BeforeClass the logger in the object under test is always the mock but see the note below for the problems with this     Class under test  import org slf4j Logger  import org slf4j LoggerFactory   public class MyClassWithSomeLogging         private static final Logger LOG   LoggerFactory getLogger MyClassWithSomeLogging class        public void doStuff boolean b            if b                LOG info  true              else               LOG info  false                         Test  import org junit AfterClass  import org junit BeforeClass  import org junit Test  import org junit runner RunWith  import org powermock core classloader annotations PrepareForTest  import org powermock modules junit4 PowerMockRunner  import org slf4j Logger  import org slf4j LoggerFactory   import static org mockito Mockito    import static org powermock api mockito PowerMockito mock  import static org powermock api mockito PowerMockito    import static org powermock api mockito PowerMockito when     RunWith PowerMockRunner class   PrepareForTest  LoggerFactory class   public class MyClassWithSomeLoggingTest        private static Logger mockLOG        BeforeClass     public static void setup             mockStatic LoggerFactory class           mockLOG   mock Logger class           when LoggerFactory getLogger any Class class    thenReturn mockLOG               Test     public void testIt             MyClassWithSomeLogging myClassWithSomeLogging   new MyClassWithSomeLogging            myClassWithSomeLogging doStuff true            verify mockLOG  times 1   info  true                Test     public void testIt2             MyClassWithSomeLogging myClassWithSomeLogging   new MyClassWithSomeLogging            myClassWithSomeLogging doStuff false            verify mockLOG  times 1   info  false                AfterClass     public static void verifyStatic             verify mockLOG  times 1   info  true            verify mockLOG  times 1   info  false            verify mockLOG  times 2   info anyString               Note  If you have two tests with the same expectation I had to do the verify in the  AfterClass as the invocations on the static are stacked up - verify mockLOG  times 2   info  true     - rather than times 1  in each test as the second test would fail saying there where 2 invocation of this  This is pretty pants but I couldn t find a way to clear the invocations  I d like to know if anyone can think of a way round this

User · Answer

Use explicit injection  No other approach will allow you  for instance to run tests in parallel in the same JVM   Patterns that use anything classloader wide like static log binder or messing with environmental thinks like logback XML are bust when it comes to testing   Consider the parallelized tests I mention   or consider the case where you want to intercept logging of component A whose construction is hidden behind api B  This latter case is easy to deal with if you are using a dependency injected loggerfactory from the top  but not if you inject Logger as there no seam in this assembly at ILoggerFactory getLogger   And its not all about unit testing either  Sometimes we want integration tests to emit logging  Sometimes we don t  Someone s we want some of the integration testing logging to be selectively suppressed  eg for expected errors that would otherwise clutter the CI console and confuse  All easy if you inject ILoggerFactory from the top of your mainline  or whatever di framework you might use   So     Either inject a reporter as suggested or adopt a pattern of injecting the ILoggerFactory  By explicit  ILoggerFactory injection rather than Logger you can support many access intercept patterns and parallelization

User · Answer

EDIT 2020-09-21  Since 3 4 0  Mockito supports mocking static methods  API is still incubating and is likely to change  in particular around stubbing and verification  It requires the mockito-inline artifact  And you don t need to prepare the test or use any specific runner  All you need to do is    Test public void name         try  MockedStatic lt LoggerFactory gt  integerMock   mockStatic LoggerFactory class             final Logger logger   mock Logger class           integerMock when    - gt  LoggerFactory getLogger any Class class    thenReturn logger           new Controller   log            verify logger  warn any              The two inportant aspect in this code  is that you need to scope when the static mock applies  i e  within this try block  And you need to call the stubbing and verification api from the MockedStatic object    Mick  try to prepare the owner of the static field too  eg    PrepareForTest  GoodbyeController class  LoggerFactory class    EDIT1   I just crafted a small example  First the controller   import org slf4j Logger  import org slf4j LoggerFactory   public class Controller       Logger logger   LoggerFactory getLogger Controller class        public void log     logger warn  quot yup quot         Then the test   import org junit Test  import org junit runner RunWith  import org powermock core classloader annotations PrepareForTest  import org powermock modules junit4 PowerMockRunner  import org slf4j Logger  import org slf4j LoggerFactory   import static org mockito Matchers any  import static org mockito Matchers anyString  import static org mockito Mockito verify  import static org powermock api mockito PowerMockito mock  import static org powermock api mockito PowerMockito mockStatic  import static org powermock api mockito PowerMockito when    RunWith PowerMockRunner class   PrepareForTest  Controller class  LoggerFactory class   public class ControllerTest         Test     public void name   throws Exception           mockStatic LoggerFactory class           Logger logger   mock Logger class           when LoggerFactory getLogger any Class class    thenReturn logger                    new Controller   log                     verify logger  warn anyString              Note the imports   Noteworthy libs in the classpath   Mockito  PowerMock  JUnit  logback-core  logback-clasic  slf4j  EDIT2   As it seems to be a popular question  I d like to point out that if these log messages are that important and require to be tested  i e  they are feature   business part of the system then introducing a real dependency that make clear theses logs are features would be a so much better in the whole system design  instead of relying on static code of a standard and technical classes of a logger  For this matter I would recommend to craft something like  a Reporter class with methods such as reportIncorrectUseOfYAndZForActionX or reportProgressStartedForActionX  This would have the benefit of making the feature visible for anyone reading the code  But it will also help to achieve tests  change the implementations details of this particular feature  Hence you wouldn t need static mocking tools like PowerMock  In my opinion static code can be fine  but as soon as the test demands to verify or to mock static behavior it is necessary to refactor and introduce clear dependencies

[java] Mocking Logger and LoggerFactory with PowerMock and Mockito

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