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JMRI Code: Unit testing with JUnit

JUnit is a system for building "unit tests" of software. Unit tests are small tests that make sure that individual parts of the software do what they're supposed to do. In a distributed project like JMRI, where there are lots of developers in only loose communication with each other, unit tests are a good way to make sure that the code hasn't been broken by a change.

For more information on JUnit, see the JUnit home page. We now use JUnit version 5 (JUnit5), although a lot of JMRI code originally had tests written in the previous versions, JUnit3 and Junit4.

A very interesting example of test-based development is available from Robert Martin's book.

All of the JMRI classes have JUnit tests available; we have decided that our Continuous Integration system will insist on that. It's good to add JUnit tests as you make changes to classes (they test your new functionality to make sure that it is working, and keeps working as other people change it later), when you have to figure out what somebody's code does (the test documents exactly what should happen!), and when you track down a bug (make sure it doesn't come back).

Running the Tests

To run the existing tests, say
   ant alltest
This will compile the test code, which lives in the "test" subdirectory of the "java" directory in our usual code distributions, and then run the tests under a GUI. (To make sure you've recompiled everything, you may want to do ant clean first)
If you know the name of your test class, or the test class for your package, you can run that directly with the "runtest" script:
   ant tests
   ./runtest.csh jmri.jmrit.powerpanel.PowerPanelTest
The first line compiles all the test code, and the second runs a specific test or test suite.
(See also how to set this up using IntelliJ)

There is also a PowerShell (Core) script available to help running tests with maven,

. Its main features are: Find detailed usage by issuing
powershell -File .\java\runtests.ps1 -?
in a console. If your console is a PowerShell console, you can issue
Get-Help .\java\runtests.ps1 -detailed
to get detailed help and instructions.

Optional Checks

There are a number of run-time optional checks that can be turned on by setting properties. We periodically run them to check on how the overall test system is working, but they're too time intensive to leave on all the time.
If true, JUnit tests will skip checking the schema of all the test XML files.
If true, JUnit tests will skip running the jython/tests scripts.
When set true, run some extra tests; usually used during code migration, where not everything is right yet but you want to be able to include tests for individual running.
If true, check for whether JUnitUtil.setUp() and JUnitUtil.teardown() follow each other int the proper sequence. Print a message if not. (This slows execution a bit due to the time needed to keep history for the message)
If true, makes jmri.util.JUnitUtil.checkSetUpTearDownSequence more verbose by also including the current stack trace along with the traces of the most recent setUp and tearDown calls.
If true, checks for any threads that have not yet been terminated during the test tearDown processing. If found, the context is logged as a warning.
If true, issues a warning if a test takes too long. The default limit is 5000 msec, but you can change it defining the jmri.util.JUnitUtil.checkTestDurationMax environment variable.
For more on setting these, see the start-up scripts page.

Controlling Test Operation

There are a number of properties that can be used to modify standard behaviour in ways that make testing easier.
When set to "true", this tells certain tests to leave windows open so that they can be used as demos or manual tests. The default is "false", clean up at the end of the test.
When set, use the specified class for the AudioFactory implementation. Setting it to will recreate the audio environment on the CI machines, which have no audio hardware available.
Override the default "tests.lcf" logging control file name.
When set, use the specified class as the default ShutDownManager. The specified class must implement the jmri.ShutDownManager interface and have a public default constructor. This is used in our standard testing infrastructure(s) to ensure that a mocked test-compatible ShutDownManager is available.
When set to "true", this skips running certain tests that should be run separately (not in the long series of tests we use for CI running) because they behave intermittently when run as part of the main test sequence. The scripts/run_flagged_tests_separately file runs these test classes separately.
If true, JUnit tests will print to stderr each JUnitUtil.setUp() call and when checkSetUpTearDownSequence is true will also print to stderr each JUnitUtil.teardown() call. This can be useful if i.e. the CI tests are hanging, and you can't figure out which test class is the problem.
Prints detailed lists of each test completed, failed and ignored to stdout. It's a lot of output, but can help track down when an obscure message was emitted or exception happened. It also can be used to see the order in which tests are being run.
Reduces the information printed during a normmal JUnit run to dots (.) for passed tests, F for failed ones, A for aborted ones (assumptions not met) and I for @Ignored ones. This is followed by a one-line summary, then more detail on failures.
For more on setting these, see the start-up scripts page.

A Note on Internationalization (I18N)

Tests check the correctness of text in GUI elements, warning messages, and other places. Many of these are internationalized, varying depending on the computer's Locale.

To avoid false failures, the Ant and Maven build control files set the locale to en_US before running tests. This covers continuous integration running, and running locally using e.g. "ant headlesstest" or "ant alltest".

The ./runtest.csh mechanism does not automatically set the locale. To do that, the easiest approach is to set the JMRI_OPTIONS environment variable via one of:

   setenv JMRI_OPTIONS "-Duser.language=en -Duser.region=US"
   export JMRI_OPTIONS="-Duser.language=en -Duser.region=US"
depending on what kind of OS and shell you're using. For more on how this works, see the page on startup scripts.

Continuous Integration Test Execution

The continuous integration environment senses changes in the code repository, rebuilds the code, performs a variety of checks. If no fatal issues are found, the continuous integration process executes the "alltest" ant target against the build to run the tests against the successful build of the code base.

Error Reporting

If a test fails during the continuous integration execution of "alltest", an e-mail is sent to the jmri-build e-mail list as well as to the developers who have checked in code which was included in the build.

You may visit the web site to subscribe to the jmri-builds e-mail list to get the bad news as quickly as possible, or monitor to view the archives of the e-mail list and see past logs. Or you can monitor the "dashboard" at the continuous integration web site.

(When the build succeeds, nothing is mailed, to cut down on traffic)

Code Coverage Reports

As part of running the tests, Jenkins accumulates information on how much of the code was executed, called the "code coverage". We use the JaCoCo tool to do the accounting. It provides detailed reports at multiple levels:

Writing Tests

By convention, we have a "test" class shadowing (almost) every real class. The "test" directory contains a tree of package directories parallel to the "src" tree. Each test class has the same name as the class to be tested, except with "Test" appended, and will appear in the "test" source tree. For example, the "jmri.Version" class's source code is in "src/jmri/", and it's test class is "jmri.VersionTest" found in "test/jmri/".

Writing Additional Tests for an Existing Class

To write additional tests for a class with existing tests, first locate the test class. (If one doesn't exist, see the section below about writing tests for a new class)

The JUnit conventions require that the test be preceeded by the "@Test" annotation:

    public void testSomething() {

In general, test methods should be small, testing just one piece of the classes operation. That's why they're called "unit" tests.

Writing Tests for a New Class

To write a test for a new class, you need to create a file that shadows your new class. For our example, consider creating a test for a new class that appears in "src/jmri/jmrix/foo/". The new test would be created in a file named "test/jmri/jmrix/foo/".

Assuming that the Foo class has a default constructor named foo(), Then the following would be minimal contents for the test/jmri/jmrix/foo/ file:


    import jmri.util.JUnitUtil;
    import org.junit.jupiter.api.BeforeEach;
    import org.junit.jupiter.api.AfterEach;
    import org.junit.jupiter.api.Test;

    import static org.assertj.core.api.Assertions.assertThat;

     * Tests for the Foo Class
     * @author  Your Name   Copyright (C) 2016
    public class FooTest {

        public void testCtor() {
            Assert.AssertNotNull("Foo Constructor Return",new foo());

        public void setUp() {

        public void tearDown() {

Note that you should be invoking jmri.util.JUnitUtil.setUp() and jmri.util.JUnitUtil.tearDown() as above.

In addition, the tearDown() method should set all member variable references to null. This is because JUnit keeps the test class objects around until all the tests are complete, so any memory you allocate in one class can't be garbage collected until all the tests are done. Setting the references to null allows the objects to be collected. (If the allocated objects have a dispose() method or similar, you should call that too). You should not reset the InstanceManager or other managers in the tearDown method; any necessary manager resets will be done automatically, and duplicating those wastes test time.

You may also choose to copy an existing test file and make modifications to suite the needs of your new class.

Writing Tests for a New Package

To write tests for an entirely new package, create a director in the jmri/tests tree that's in the analogous place to your new code directory. For example, if you're creating java/src/jmri/jmrit/foo, create a java/test/jmri/jmrit/foo directory and place your *Test classes there.

Key Test Metaphors

AssertJ Tools

The fluent assertions in the AssertJ core Assertions classes can tooling for many useful idioms that go well beyond the simple JUnit Assert class tools: See below for info on using AssertJ with Swing.

Handling Log4J Output FromTests

JMRI uses Log4j to handle logging of various conditions, including error messages and debugging information. Tests are intended to run without error or warning output, so that it's immediately apparent from an empty standard log that they ran cleanly.

Log4j usage in the test classes themselves has two aspects:

  1. It's perfectly OK to use log.debug(...) statements to make it easy to debug problems in test statements. can be used sparingly to indicate normal progress, because it's normally turned off when running the tests.
  2. In general, log.warn or log.error should only be used when the test then goes on to trigger a JUnit assertion or exception, because the fact that an error is being logged does not show up directly in the JUnit summary of results.

On the other hand, you might want to deliberately provoke errors in the code being tested to make sure that the conditions are being handled properly. This will often produce log.error(...) or log.warn(...) messages, which must be intercepted and checked.

To allow this, JMRI runs it's using tests with a special log4j appender, which stores messages so that the JUnit tests can look at them before they are forwarded to the log. There are two aspects to making this work:

  1. All the test classes should include common code in their setUp() and tearDown() code to ensure that log4j is properly initiated, and that the custom appender is told when a test is beginning and ending.
        public void setUp() throws Exception {
        public void tearDown() throws Exception {
  2. When a test is deliberately invoking a message, it should then use JUnitAppender class methods to check that the message was created. For example, if the class under test is expected to do
        log.warn("Provoked message");
    the invoking test case should follow the under-test calls that provoke that with the line:
        jmri.util.JUnitAppender.assertWarnMessage("Provoked message");

    It will be a JUnit error if a log.warn(...) or log.error(...) message is produced that isn't matched to a JUnitAppender.assertWarnMessage(...) call.

  3. The Log4JUtil.warnOnce(..) requires some special handling in tests. We want each test to be independent, so we reset the "want only once" logic early in the JUnitUtil.setUp() that's routinely invoked @BeforeEach the tests. This means that the first invocation, and only the first invocation, for each message will be logged.
  4. We want to make it easy to add a Log4JUtil.deprecationWarning call when a method is deprecated. This will log a message the first time it's invoked. We want to warn that deprecated code is being invoked during normal operation, so this is normally becomes a Log4JUtil.warnOnce(..) call. When you see those warnings messages, you should remove them by completing the migration away from the deprecated method.

    The one exception is during unit and CI testing of the actual deprecated method. We want to keep those tests around until the deprecated method is finally removed. That ensures it keeps working until it's deliberately removed, and not inadvertently broken in the meantime. In this case, you should turn off the Log4JUtil.deprecationWarning in just that test method using Log4JUtil.setDeprecatedLogging(false) before invoking the deprecated method. (You can also do an JUnitAppender.assertWarn for all the messages emitted, but it's easier to just turn them off.)

Note: Our CI test executables are configured to fail if any FATAL or ERROR messages are emitted instead of being handled. This means that although you can run your tests successfully on your own computer if they're emitting ERROR messages, but you won't be able to merge your code into the common repository until those are handled. It's currently OK to emit WARN-level messages during CI testing, but that will also be restricted (cause the test to fail) during tne 4.15.* development series, so please suppress or handle those messages too.

Resetting the InstanceManager

If you are testing code that is going to reference the InstanceManager, you should clear and reset it to ensure you get reproducible results.

Depending on what managers your code needs, your setUp() implementation could start with:



(You can omit the initialization managers not needed for your tests) See the jmri.util.JUnitUtil class for the full list of available ones, and please add more if you need ones that are not in JUnitUtil yet.

Your tearDown() should end with:


Working with a ShutDownManager

During testing, your code might need a ShutDownManager. There are several points to consider:

Working with a Timebase

A simple, internal Timebase is provided by default when one is requested from the InstanceManager. You don't have to prepare one in advance. But please note that simple Timebase is initialized to Right Now, and starts in a running state. To get consistent results from your tests, you should instead set it to a consistent time (so e.g. AM/PM branches always go the same way) and to not be running (so that results don't vary with run time). To do that:
    Timebase clock = InstanceManager.getDefault(jmri.Timebase.class);
    clock.setTime(java.time.Instant.EPOCH);  // just a specific time
After this, when you code picks up a Timebase instance, it'll get this properly prepared one.

Working with Listeners

JMRI is a multi-threaded application. Listeners for JMRI objects are notified on various threads. Sometimes you have to wait for that to take place.

If you want to wait for some specific condition to be true, e.g. receiving a reply object, you can use a waitFor method call which looks like:

    JUnitUtil.waitFor(()->{reply!=null}, "reply didn't arrive");
The first argument is a lambda closure, a small piece of code that'll be evaluated repeatedly until true. The String second argument is the text of the assertion (error message) you'll get if the condition doesn't come true in a reasonable length of time.

Waiting for a specific result is fastest and most reliable. If you can't do that for some reason, you can do a short time-based wait:

This uses a nominal delay. But you might want to consider the structure of either your code (that you're testing) or the test itself: If you can't tell whether it succeeded, what's the purpose of the operation?

Note that this should not be used to synchronize with Swing threads. See the Testing Swing Code section for that.

In general, you should not have calls to sleep(), wait() or yield() in your code. Use the JUnitUtil and Jemmy support for those instead.

Working with Threads

(See a following section for how to work with Swing (GUI) objects and the Swing/AWT thread)

Some tests will need to start threads, for example to test signal controls or aspects of layout I/O.

General principles your tests must obey for reliable operation:

For example, if creating a thread based on AbstractAutomat, you can check the start with:

    AbsractAutomat p = new MyThreadClass();
    JUnitUtil.waitFor(()->{return p.isRunning();}, "logic running");
and ensure termination with
    JUnitUtil.waitFor(()->{return !p.isRunning();}, "logic stopped");

Please make sure your unit tests clean up after themselves! They should not leave any threads running. Any threads they start should have either terminated normally by the end of the test (don't let them just time out and crash later during some other test!) or you should add code to terminate them.

You can check whether you've left any threads running by setting the jmri.util.JUnitUtil.checkRemnantThreads environment variable to true, with i.e.

setenv JMRI_OPTIONS -Djmri.util.JUnitUtil.checkRemnantThreads=true
or the equivalent for your computer type. This tells the JUnitUtil.tearDown() method to check for any (new) threads that are still running at the end of each test. This check is a bit time-intensive, so we don't leave it on all the time.

Tools like heap dumps, thread dumps, and the jvisualvm browser can help you see what's being left over by your tests. But they must be used while the JVM is still running, and it usually terminates right after the tests. To prolong the JVM life, add an instance of jmri.util.TestWaitsForever at the end of your PackageList list of tests. TestWaitsForever does what it says on the tin: waits forever, allowing you to look at the state of the JVM. When you're done, you have to kill the test job manually.

Testing I/O

Some test environments don't automatically flush I/O operations such as streams during testing. If you're testing something that does I/O, for example a TrafficController, you'll need to add "flush()" statements on all your output streams. (Having to wait a long time to make a test reliable is a clue that this is happening somewhere in your code)

Temporary File Creation in Tests

Test cases which create temporary files must be carefully created so that there will not be any problems with file path, filesystem security, pre-existence of the file, etc. These tests must also be written in a way that will operate successfully in the continuous integration build environment. And the temporary files should not become part of the JMRI code repository. This section discusses ways to avoid these types of problems.

If you need a temporary file or directory, you can use the JUnit5 TempDir extension to create a file or directory.

The @TempDir annotation can be applied to test class fields of type File or Path.

    protected File folder;

Or as dependency injected values on methods

    public void testFoo(@TempDir File folder){

You then reference "folder" in your test code:

        // create a temporary file
        File randomNameFile = folder.newFile();
        // create a temporary directory
        File randomNameDir = folder.newFolder();
JUnit will make sure the file or folder is removed afterwards regardless of whether the test succeeds or fails. For more information on this, see the Javadoc for TemporaryDir.

JUnit 5 Extensions

JUnit 4 used Rules to provide special behavior required in certain test extensions. JUnit 5 has replaced rules with annotation based extensions. Extensions may be applied at the class level, the method level, and sometimes to individual fields. The following is a list of a few extensions we have utilized in testing JMRI.
  1. which is used to create temporary folders and files as described previously
  2. @org.junit.jupiter.api.Timeout which is used to set a timeout. the @Timeout annotation takes a time as a parameter and can optionally takes units for the given time. The default time unit is seconds, so @Timeout (2) creates a 2 second timeout. The @Timeout annotation may be used on the class or on individual test methods within the class. When applied to the class, the effect is applying the timeout to all @Test annotated methods within the class. described previously

JUnit Rules

JUnit4 added the concept of "Rules" that can modify the execution of tests. They work at the class or test level to modify the context JUnit uses for running the classes tests. Generally, you start by creating one:
    public final TemporaryFolder tempFolder = new TemporaryFolder();

Some standard JUnit rules you might find useful:

Timeout - limit duration

The Timeout rule imposes a timeout on all test methods in a class.
    public org.junit.rules.Timeout globalTimeout = org.junit.rules.Timeout.seconds(10);

Note that you can also add a timeout option to an individual test via an argument to the @Test annotation. For example,

will put a 2 second (2,000 milliseconds) timeout on that test. If you use both the rule and the option, the option will control the behavior. For a bit more info, see the JUnit Timeouts for Tests page.

RetryRule - run test several times

JMRI has jmri.util.junit.rules.RetryRule which can rerun a test multiple times until it reaches a limit or finally passes. Although it's better to write reliable tests, this can be a way to make the CI system more reliable while you try to find out why a test isn't reliable.

For a working example, see java/test/jmri/jmrit/logix/

Briefly, you just add the lines

    import jmri.util.junit.rules.RetryRule;

    public RetryRule retryRule = new RetryRule(3);  // allow 3 retries
to your test class. This will modify how JUnit handles errors during all of the tests in that class.

Tools for Controlling JUnit tests

  • Tags and Filters - useful ones in our case could be headless/not headless, hardware specific (loco buffer attached, NCE PowerPro attached, etc)
  • JUnit 5 provides a collection of conditional annotations. JMRI makes extensive use of @DisabledIfSystemProperty to conditionally ignore a test. For example, a test that would fail in a headless environment should be ignored in headless mode. Adding the following annotation to the tet method
    @DisabledIfSystemProperty(named ="java.awt.headless", matches ="true")
    will cause the test to be ignored in headless mode. If a whole class is to be disable din headless mode, this same annotation may be applied to the test class.
  • @Disabled - mark a test to be unconditionally ignored. For example, a test that fails because it isn't fully implemented yet can be marked to be ignored:
            @org.junit.jupiter.api.Disabled("not done yet")
            @jmri.util.junit.annotations.ToDo("Need to create some mock Framistat Objects")
            public void notDoneYet() {
                // some code that compiles but doesn't run

    You should provide the reason for ignoring this test in the @Disabled argument. @Disabled without an argument will compile, but Jenkins will mark it as an error.

    Also note the @jmri.util.junit.annotations.ToDo annotation which indicates that this needs work and provides some more information about what needs to be done. The @ToDo is required when an empty test is provided to ensure that the parent class test doesn't run, but the parent class is applicable to the class under test.

    In general, we'd rather have working tests rather than ignored ones, so we track the number that have been ignored in a Jenkins job, see the image to the right.

  • On the other hand, sometimes a test super class (i.e. some abstract base) requires implementation of a test method that's not applicable to this particular concrete test class. It might, for example, test a feature or message that's not applicable for a specific system's hardware. In that case, you provide a null body to do nothing, and mark the test as not applicable with the @jmri.util.junit.annotations.NotApplicable annotation like this:
            @jmri.util.junit.annotations.NotApplicable("System X doesn't use Framistat Objects")
            public void testFramistatUsage() {}

    Testing Swing Code

    AWT and Swing code runs on a separate thread from JUnit tests. Once a Swing or AWT object has been displayed (via show() or setVisible(true)), it cannot be reliably accessed from the JUnit thread. Even using the listener delay technique described above isn't reliable.

    For the simplest possible test, displaying a window for manual interaction, it's OK to create and invoke a Swing object from a JUnit test. Just don't try to interact with it once it's been displayed!

    Because we run tests in "headless" mode during the continuous integration builds, it's important that tests needing access to the screen are annotated with:

    @DisabledIfSystemProperty(named ="java.awt.headless", matches ="true")

    This will run the test only when a display is available.

    GUI tests should close windows when they're done, and in general clean up after themselves. If you want to keep windows around so you can manipulate them, e.g. for manual testing or debugging, you can use the jmri.demo system parameter to control that:

            if (!System.getProperty("jmri.demo", "false").equals("false")) {

    For many tests, you'll both make testing reliable and improve the structure of your code by separating the GUI (Swing) code from the JMRI logic and communications. This lets you check the logic code separately, but invoking those methods and checking the state them update.

    For more complicated GUI testing, the AssertJ and Jemmy tools are preferred.

    Using AssertJ with Swing

    The AssertJ-Swing classes can tooling for many useful idioms that can be helpful when testing Swing code.

    Using Jemmy

    For more information on Jemmy, please see the tutorial Wiki page and the Jemmy Javadoc. There are samples on the NetBeans pages.

    Locating GUI Items using Jemmy

    Jemmy must be able to find the objects on the screen. Jemmy Operators are generally used to both locate and manipulate items on the screen.

    Here are a few tips for locating items with Jemmy:

    • Some of the Jemmy Operator Constructors allow leaving off an identifier. If there is only one object of a given type on the screen at any time, it is acceptable to use this version of the constructor, but the test may be fragile.
    • It is easiest to find objects if they have a unique identifier. In the case where no unique identifier exists, Jemmy provides a version of most searches that allows you to specify an ordinal index. Using these may result in tests that break when GUI elements are added or removed from the frame.
    • If an item contains its own text (Buttons, for example), it is recommended you use the text to search for a component.
    • If an item does not contain its own description, but the GUI contains a JLabel describing that component, be certain the JLabel's LabelFor property is set. A Jemmy JLabelOperator can then be used to find the label, and retrieve the object.
    • When looking for a button, window or other item by it's label text, the default Jemmy string comparison is a case insensitive caption.contains(match). If ce is true, then the equals(..) method is used. The ccs option controls case sensitivity.
    • Jemmy's ComboBoxOperator selectItem(String) can only reliably set the value of JComboBox<String>, (i.e. its unreliable with JComboBox<NamedBean>), so that method needs to be replaced with setSelectedItem(Object)
    • Jemmy's clearText() and typeText(String) methods can't handle JTextComponents with complex borders (such as used by SystemNameValidator and NamedBeanComboBox); those methods need to be replaced with setText(String). Please note that setText just sets the text value in the text entry box while typeText types in every single character. If you are testing a text entry field with a keyListener attached, the keyListener never executes with setText.

    Example of Closing a Dialog Box

    If you want to test a method that pops a have a JDialog box with a title (in top bar of the dialog window) of "Foo Warning" and an "OK" button to close it, put this in your JUnit test:
            new Thread(() -> {
                // constructor for d will wait until the dialog is visible
                JDialogOperator d = new JDialogOperator("Foo Warning");
                JButtonOperator bo = new JButtonOperator(d,"OK");
                jmri.util.ThreadingUtil.runOnGUI(() -> {bo.push();});
    The thread is started before your code runs and starts Jemmy looking for the Dialog box. Once it appears, Jemmy will push the "OK" button. You can't put the Jemmy calls in advance: They'll wait forever for the dialog to appear, and never proceed to your code to show the dialog. And you can't put them after the call, because your call won't exist until somebody presses "OK".

    Jemmy timeouts

    Jemmy has an extensive system of built-in timeouts. It'll wait to perform an operation until e.g. the requested button or menu is on the screen, but will eventually timeout if it can't find it. In that case it throws a org.netbeans.jemmy.TimeoutExpiredException with some included diagnostic test. Please don't catch this exception: the problem here is not the exception, it's that Jemmy wasn't able to do what you asked. That's the thing that needs to be debugged.

    If you want to change one of Jemmy's timeouts, do

            myMenuOperator.getTimeouts().setTimeout("JMenuOperator.WaitBeforePopupTimeout", 30L);
    where "myMenuOperator" is a reference to a Jemmy operator object, 30L is the new value (a long) in milliseconds, and the particular timeout name comes from the Javadoc. Sometimes, setting the "WaitBeforePopupTimeout" from it's default of zero to a few milliseconds can improve the reliability of tests. Also, setting "JMenuOperator.WaitPopupTimeout" and "ComponentOperator.WaitComponentTimeout" to a lower value from their defaults of 60000L (a minute) can speed work when you're trying to debug the cause of a timeout.

    If you change a timeout, you must set it back to the original value (which you had earlier saved) in your @AfterEach routine. If you leave it changed, you're likely to cause problems for other test routines.

    Jemmy hints and issues

    Actions like work like clicking on a real screen: if the click target isn't the foremost component when the click happens, the click will go to some other component. This is particularly annoying when you're running a long series of tests on your own computer will doing other work, as pushing test windows to the background will likely cause (false-negative) failures.

    If your test thread invokes a method that causes a lot of Swing/AWT activity, that might not all be complete when the method returns. For example, if you create a JFrame and either explicitly or implicitly call pack(), that starts the Swing thread working on that frame; that can proceed in parallel to the return to the test thread. If the test thread will continue to do more Swing operations, like create and pack another frame, you'll have problems unless you either:

    • Do all those operations on the GUI thread by enclosing them in jmri.util.ThreadingUtil.runOnGUI calls so that the entire sequence of operations is done on the Swing. This is what's normally done in Swing applications, and it's a test of the real operation.
    • But Assert operations need to be done on the test thread, so if you want to intermix Swing and test operations you can synchronize the threads by calling
              new org.netbeans.jemmy.QueueTool().waitEmpty();
      on the test thread.

      In some rare cases, you need to wait for the Swing queue to stay empty for a non-zero interval. In that case, use waitEmpty(20). where the argument (in this example 20) is how many milliseconds the queue has to remain empty before proceeding. We're not sure what the best value is; see JMRI Issue #5321 and NetBeans bug tracker 36665 for some background discussion. Briefly, since things like flashing cursors fire Swing events, the queue doesn't stay idle forever once the primary work is done. A long wait-for-empty value may never occur.

    Testing Script Code

    JMRI ships with sample scripts. This section discussions how you can write simple tests for those to ensure they keep working.

    Testing Jython sample scripts

    Test scripts can be placed in jython/test are automatically invoked by java/test/jmri/jmrit/jython/

    See the sample for syntax, including examples of how to signal test failures.

    In the future, this could be extended to pick up files automatically, to support xUnit testing, etc.


    JUnit uses a custom classloader, which can cause problems finding singletons and starting Swing. If you get the error about not being able to find or load a class, suspect that adding the missing class to the test/junit/runner/ file would fix it.

    As a test only, you can try setting the "-noloading" option in the main of whichever test class you're having trouble with:

        static public void main(String[] args) {
                String[] testCaseName = {"-noloading", LogixTableActionTest.class.getName()};

    Please don't leave "-noloading" in place, as it prevents people from rerunning the test dynamically. Instead, the right long-term fix is to have all classes with JUnit loader issues included in the test/junit/runner/ file. JUnit uses those properties to decide how to handle loading and reloading of classes.