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Testing JabRef

In JabRef, we mainly rely on basic JUnit unit tests to increase code coverage.

General hints on tests

Imagine you want to test the method format(String value) in the class BracesFormatter which removes double braces in a given string.

  • Placing: all tests should be placed in a class named classTest, e.g. BracesFormatterTest.
  • Naming: the name should be descriptive enough to describe the whole test. Use the format methodUnderTest_ expectedBehavior_context (without the dashes). So for example formatRemovesDoubleBracesAtBeginning. Try to avoid naming the tests with a test prefix since this information is already contained in the class name. Moreover, starting the name with test leads often to inferior test names (see also the Stackoverflow discussion about naming).
  • Test only one thing per test: tests should be short and test only one small part of the method. So instead of

      void format() {
          assertEqual("test", format("test"));
          assertEqual("{test", format("{test"));
          assertEqual("test", format("test}}"));

    we would have five tests containing a single assert statement and named accordingly (formatDoesNotChangeStringWithoutBraces, formatDoesNotRemoveSingleBrace, , etc.). See JUnit AntiPattern for background.

  • Do not just test happy paths, but also wrong/weird input.
  • It is recommended to write tests before you actually implement the functionality (test driven development).
  • Bug fixing: write a test case covering the bug and then fix it, leaving the test as a security that the bug will never reappear.
  • Do not catch exceptions in tests, instead use the assertThrows(Exception.class, () -> doSomethingThrowsEx()) feature of junit-jupiter to the test method.


IntelliJ has build in test coverage reports. Choose “Run with coverage”.

For a full coverage report as HTML, execute the gradle task jacocoTestReport (available in the “verification” folder in IntelliJ). Then, you will find <build/reports/jacoco/test/html/index.html> which shows the coverage of the tests.

Lists in tests

Instead of



assertEquals(List.of(), actualList);

Similarly, to compare lists, instead of following code:

assertEquals(2, actualList.size());
assertEquals("a", actualList.get(0));
assertEquals("b", actualList.get(1));

use the following code:

assertEquals(List.of("a", "b"), actualList);

BibEntries in tests

  • Use the assertEquals methods in BibtexEntryAssert to check that the correct BibEntry is returned.

Files and folders in tests

If you need a temporary file in tests, use the @TempDir annotation:

class TestClass{

  void deletionWorks(@TempDir Path tempDir) {

to the test class. A temporary file is now created by Files.createFile(path). Using this pattern automatically ensures that the test folder is deleted after the tests are run. See for more details.

Loading Files from Resources

Sometimes it is necessary to load a specific resource or to access the resource directory

Path resourceDir = Paths.get(MSBibExportFormatTestFiles.class.getResource("MsBibExportFormatTest1.bib").toURI()).getParent();

When the directory is needed, it is important to first point to an actual existing file. Otherwise the wrong directory will be returned.

Preferences in tests

If you modify preference, use following pattern to ensure that the stored preferences of a developer are not affected:

Or even better, try to mock the preferences and insert them via dependency injection.

public void getTypeReturnsBibLatexArticleInBibLatexMode() {
     // Mock preferences
     PreferencesService mockedPrefs = mock(PreferencesService.class);
     GeneralPreferences mockedGeneralPrefs = mock(GeneralPReferences.class);
     // Switch to BibLatex mode

     // Now test
     EntryTypes biblatexentrytypes = new EntryTypes(mockedPrefs);
     assertEquals(BibLatexEntryTypes.ARTICLE, biblatexentrytypes.getType("article"));

To test that a preferences migration works successfully, use the mockito method verify. See PreferencesMigrationsTest for an example.

Database tests


To quickly host a local PostgreSQL database, execute following statement:

docker run -d -e POSTGRES_USER=postgres -e POSTGRES_PASSWORD=postgres -e POSTGRES_DB=postgres -p 5432:5432 --name db postgres:10 postgres -c log_statement=all

Set the environment variable DBMS to postgres (or leave it unset)

Then, all DBMS Tests (annotated with @org.jabref.testutils.category.DatabaseTest) run properly.


A MySQL DBMS can be started using following command:

docker run -e MYSQL_ROOT_PASSWORD=root -e MYSQL_DATABASE=jabref -p 3800:3307 mysql:8.0 --port=3307

Set the environment variable DBMS to mysql.

Advanced testing and further reading

On top of basic unit testing, there are more ways to test a software:

Type Techniques Tool (Java) Kind of tests Used In JabRef
Functional Dynamics, black box, positive and negative JUnit-QuickCheck Random data generation No, not intended, because other test kinds seem more helpful.
Functional Dynamics, black box, positive and negative GraphWalker Model-based No, because the BibDatabase doesn’t need to be tests
Functional Dynamics, black box, positive and negative TestFX GUI Tests Yes
Functional Dynamics, black box, negative Lincheck Testing concurrent algorithms No
Functional Dynamics, white box, negative PIT Mutation No
Functional Dynamics, white box, positive and negative Mockito Mocking Yes
Non-functional Dynamics, black box, positive and negative JETM, Apache JMeter Performance (performance testing vs load testing respectively) No
Structural Static, white box CheckStyle Constient formatting of the source code Yes
Structural Dynamics, white box SpotBugs Reocurreing bugs (based on experience of other projects) No