JUnit5: Parameterized Tests

As we studied in Junit5 in part1 and part2. Junit5 is very impressive in the extension model and architectural style, also the Junit5 Assumptions. The another best aspect about junit5 is compatibility with a lambda expression. In this section let us start looking for Junit5 parameterized tests.

The term parameter is often used to refer to the variable as found in the function definition, while argument refers to the actual input passed.

Maven Dependency:


Gradle Dependency:


The basic difference while annotating the method instead of start by declaring a test method on @ParameterizedTest instead of @Test for a parameterised test. There are few scenarios where we want to pass values dynamically as method argument and a unit test that for this type of a scenario parameterized test cases are useful.

It looks below code is incomplete. From where this word value will come. how would JUnit know which arguments the parameter word should take? And indeed, Jupiter engine does not execute the test and instead throw a PreconditionViolationException.

void parameterizedTest(String word) {
Configuration error: You must provide at least
one argument for this @ParameterizedTest

Let us start correcting the above exception.

@ValueSource(strings = {"JUnit5 ParamTest" , "Welcome"})
void withValueSource(String word) {

Now above code will successfully get executed. This is just a simple use case but in real life project, you need more tools for that purpose you should know in detail of @ValueSource annotation.


@ValueSource annotation is to provide a source of argument to the parameterized test method. The source can be anything like single value, an array of values, null source, CSV file, etc. As we have seen in the above example @ValueSource annotation, we can pass an array of literal values to the test method.

public class Strings {
     public static boolean isEmptyString(String str) {
         return str == null || str.trim().isEmpty();
// Test case for the above method could be 
@ValueSource(strings = {"", "  ","Non Empty"})
 void isEmptyStringReturnTrueForNullOrBlankStrings(String str) {

Limitations of value sources:

1. It only support the following data types.

2. We can pass only one argument to the test method each time.

3. We can not pass null as a argument to the test method.

  • short (with the shorts attribute)
  • byte (with the bytes attribute)
  • int (with the ints attribute)
  • long  (with the longs attribute)
  • float (with the floats attribute)
  • double (with the doubles attribute)
  • char (with the chars attribute)
  • java.lang.String (with the strings attribute)
  • java.lang.Class (with the classes attribute)

@NullSource and @EmptySource:

We can pass a single null value to a parameterized test method using @NullSource and its not for the primitive data types.

@EmptySource passes a single empty argument and you can use empty source for collection types and for array too.

In order to pass both null and empty values, we can use the composed @NullAndEmptySource annotation

@ValueSource(strings = {” “, “\t”, “\n”})
void isEmptyStringReturnTrueForAllTypesOfBlankStrings(String input) {


The name implies its self, if we want to test different values from an enumeration, we can use @EnumSource.

void getValueForADay_IsAlwaysBetweenOneAndSeven(WeekDay day) {
int dayNumber = day.getValue();
assertTrue(dayNumber >= 1 && dayNumber <= 7);

We can filter out a few days by using the names attribute of enum. @EnumSource annotation has option to select enum constant mode, you can either include and exclude too using EnumSource.Mode.EXCLUDE.

We can pass a string literal and regular expression both to the names attribute

Reference Document


We need argument sources capable of passing multiple arguments. As we know @ValueSource and @EnumSource are only allowing one argument each time. In real life project we want to read row input values manipulate those and unit test those for that purpose @CsvSource

@CsvSource(value = {“juniT:junit”, “MaN:man”, “Java:java”}, delimiter = ‘:’)
void toLowerCaseValue(String input, String expected) {
String actualValue = input.toLowerCase();
assertEquals(expected, actualValue);

In the above example you have key value pair with colon as a delimiter, we can also pass CSV file as a resource argument too:

//CSV file

@CsvFileSource(resources = “/testdata.csv”, numLinesToSkip = 1)
void toUpperCaseValueCSVFile(String input, String expected) {
String actualValue = input.toUpperCase();
assertEquals(expected, actualValue);

resources attribute represents the CSV file resources on the classpath and we can pass multiple CSV files too. Let us take few more examples

“2019-09-21, 2018-09-21”,
“null, 2018-08-15”,
“2017-04-01, null”
void shouldCreateValidDateRange(LocalDate startDate, LocalDate endDate) {
new DateRange(startDate, endDate);

“2019-09-21, 2017-09-21”,
“null, null”
void shouldNotCreateInvalidDateRange(LocalDate startDate, LocalDate endDate) {
assertThrows(IllegalArgumentException.class, () -> new DateRange(startDate, endDate));

When you are executing above programming you will end up getting exception.

org.junit.jupiter.api.extension.ParameterResolutionException: Error converting parameter at index 0: Failed to convert String “null” to type java.time.LocalDate

The null value isn’t accepted in @ValueSource or@CsvSource.

Method Source:

The @ValueSource and @EnumSource and pretty simple and has one limitation they won’t support complex types. MethodSource allows providing complex argument source. MehtodSource annotation takes the name of a method as an argument needs to match an existing method that returns Steam type.

void withMethodSource(String word, int length) { }

private static Stream wordsWithLength() {
return Stream.of(
Arguments.of(“JavaTesting”, 10),
Arguments.of(“JUnit 5”, 7));

When we won’t provide a name for the @MethodSource, JUnit will search for a source method with the same name as the parameterized test  method.

void wordsWithLength(String word, int length) { }

Custom Argument Provider:

As of now, we have covered inbuilt argument provider but in few scenarios, this doesn’t work for you then Junit provides custom argument provider. You can create your own source, argument provider. To achieve this we have to implement an interface called ArgumentsProvider.

public interface ArgumentsProvider {
Stream<? extends Arguments> provideArguments(
    ContainerExtensionContext context) throws Exception;


For this, we have just test with a custom empty String provider.

class EmptyStringsArgumentProvider implements ArgumentsProvider {

public Stream<? extends Arguments> provideArguments(ExtensionContext context) {
    return Stream.of( 
      Arguments.of("   "),
      Arguments.of((String) null) 

We can use this custom argument a provider using @ArgumentSource annotation.

void isEmptyStringsArgProvider(String input) {


As part of this article, we have discussed Parameterised test cases and argument provider in bits and pieces and some level of custom argument provider using ArgumentsProvider interface and @ArgumentsSource.

There are different source provider from primitive to CSV and MethodSource provider. This is for now.