Junit5 @ParameterizedTest How to pass array as one of parameter

@CsvSource uses implicit conversion to convert CSV values to primitives, Enums or Dates. For other types like Arrays, you need explicit conversion.

Assuming you have a CSV annotation in a format like @CsvSource("abc, 123, 'foo, bar'"), you can implement an argument converter like this to treat the last CSV column as an array:

import org.junit.jupiter.params.converter.ArgumentConversionException;
import org.junit.jupiter.params.converter.SimpleArgumentConverter;

public class StringArrayConverter extends SimpleArgumentConverter {

    @Override
    protected Object convert(Object source, Class<?> targetType) throws ArgumentConversionException {
        if (source instanceof String && String[].class.isAssignableFrom(targetType)) {
            return ((String) source).split("\\s*,\\s*");
        } else {
            throw new IllegalArgumentException("Conversion from " + source.getClass() + " to "
                                               + targetType + " not supported.");
        }
    }

}

Then you can use that converter on the third argument:

@ParameterizedTest
@CsvSource("abc, 123, 'foo, bar'")
void test(String column1, int column2, @ConvertWith(StringArrayConverter.class) String[] column3) {
    assertEquals(column1, "abc");
    assertEquals(column2, 123);
    assertEquals(column3[0], "foo");
    assertEquals(column3[1], "bar");
}

You can easily do something like this:

@DisplayName("Should rotate successfully")
@ParameterizedTest()
@CsvSource({
        "'[0, 0, 0]', 5, '[0, 0, 0]', false",
})
void givenAnArrayAndAShiftSize_ShouldSuccesfullyRotateOrReturnFalse(String arrayStr, int shiftSize,
        String expectedArrayStr, boolean expecetedRotated) {

    var window = Arrays.asList(arrayStr.replace("[", "").replace("]", "").split(","))
            .stream()
            .mapToLong(c -> Long.parseLong(c.toString().trim()))
            .toArray();

    var result = Arrays.asList(expectedArrayStr.replace("[", "").replace("]", "").split(","))
            .stream()
            .mapToLong(c -> Long.parseLong(c.toString().trim()))
            .toArray();

    var rotated = Utils.shiftIfSizeIsValid(window, shiftSize);

    assertEquals(expecetedRotated, rotated);

    for (int i = 0; i < window.length; i++) {
        assertEquals(result[i], window[i]);
    }
}

It is simpler and more readable.

With a little ingenuity, we can convert to almost any iterable with full generic support, including primitive and wrapper type arrays.

The following implementation is from my open source library jdata.

I let jackson-databind do all the heavy lifting. It has the added advantage that I get to use the familiar notation of JSON list in my tests instead of some homegrown weirdity.

Note that the following code uses constructs from Java 17, such as Text Blocks and Pattern Matching for instanceof.

Converter:

package junit;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.junit.jupiter.params.converter.ArgumentConversionException;
import org.junit.jupiter.params.converter.SimpleArgumentConverter;

public class IterableConverter extends SimpleArgumentConverter {
  private static final ObjectMapper MAPPER = new ObjectMapper();

  @Override
  protected Object convert(Object source, Class<?> targetType) throws ArgumentConversionException {
    if (source instanceof String s) {
      try {
        return MAPPER.readValue(s, targetType);
      } catch (JsonProcessingException jpe) {
        throw new ArgumentConversionException(jpe.getMessage(), jpe);
      }
    } else {
      throw new ArgumentConversionException("Can only convert from String");
    }
  }
}

Test:

import junit.IterableConverter;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.converter.ConvertWith;
import org.junit.jupiter.params.provider.CsvSource;

class MyTests {
  @ParameterizedTest
  @CsvSource(
      delimiter = '|',
      textBlock =
          """
    [5,7,7,8,8,10] | 8 | [3, 4]
    [5,7,7,8,8,10] | 6 | [-1,-1]
    [] | 0 | [-1,-1]
    [1] | 0 | [-1,-1]
      """)
  public void testStuff(
      @ConvertWith(IterableConverter.class) int[] nums,
      int target,
      @ConvertWith(IterableConverter.class) int[] expected) {
    // test code;
  }
}