A JUnit 5 display name generator for JUnit 5.4 or above.

CamelCastDisplayNameGenerator.java

import org.junit.jupiter.api.DisplayNameGenerator;

import java.lang.reflect.Method;

import static java.lang.Character.*;

/**
 * Change the camelcase or underscore method name into a readable display name
 *
 * @author せいうはん (Employee ID: 17092068)
 * @version 3.0.0, 2018-12-24 17:32
 * @since 3.0.0, 2018-12-24 17:32
 */
public class CamelCastDisplayNameGenerator implements DisplayNameGenerator {

    private static final DisplayNameGenerator internal = new DisplayNameGenerator.Standard();

    @Override
    public String generateDisplayNameForClass(Class<?> testClass) {
        return internal.generateDisplayNameForClass(testClass);
    }

    @Override
    public String generateDisplayNameForNestedClass(Class<?> nestedClass) {
        return internal.generateDisplayNameForNestedClass(nestedClass);
    }

    @Override
    public String generateDisplayNameForMethod(Class<?> testClass, Method testMethod) {
        String methodName = testMethod == null ? "" : removeExtraClassTag(testMethod.getName());
        return camelToText(methodName).replaceAll("_", " ");
    }

    /**
     * This method was copy from https://github.com/krasa/StringManipulation
     */
    @SuppressWarnings("squid:S3776")
    private static String camelToText(String text) {
        StringBuilder builder = new StringBuilder();
        char lastChar = ' ';
        for (char c : text.toCharArray()) {
            char nc = c;

            if (isUpperCase(nc) && !isUpperCase(lastChar)) {
                if (lastChar != ' ' && isLetterOrDigit(lastChar)) {
                    builder.append(" ");
                }
                nc = Character.toLowerCase(c);
            } else if (isDigit(lastChar) && !isDigit(c)) {
                if (lastChar != ' ') {
                    builder.append(" ");
                }
                nc = Character.toLowerCase(c);
            }

            if (lastChar != ' ' || c != ' ') {
                builder.append(nc);
            }
            lastChar = c;
        }
        return builder.toString();
    }

    /**
     * Kotlin based test sometime would have some extra module name be appended to the test method name.
     * We just need drop them for clean display name.
     */
    private String removeExtraClassTag(String name) {
        String nonNullName = name == null ? "" : name;
        if (nonNullName.contains("$")) {
            return nonNullName.substring(0, nonNullName.indexOf('$'));
        } else {
            return nonNullName;
        }
    }
}

CamelCastDisplayNameGeneratorTest.java

import org.junit.jupiter.api.DisplayNameGeneration;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestInfo;

import static org.junit.jupiter.api.Assertions.assertEquals;

/**
 * @author せいうはん (Employee ID: 17092068)
 */
@SuppressWarnings({"squid:S1192", "squid:S00100"})
@DisplayNameGeneration(CamelCastDisplayNameGenerator.class)
class CamelCastDisplayNameGeneratorTest {

    @Test
    void camelCaseCouldBeConvertToA_MoreBetterDisplayName(TestInfo testInfo) {
        assertEquals(
            "camel case could be convert to a more better display name",
            testInfo.getDisplayName()
        );
    }

    @Test
    void underscore_could_be_transform_to_display_name(TestInfo testInfo) {
        assertEquals(
            "underscore could be transform to display name",
            testInfo.getDisplayName()
        );
    }

    @Test
    void anything_after_dollar_in_method_name_would_be_removed$thisWouldBeRemove(TestInfo testInfo) {
        assertEquals(
            "anything after dollar in method name would be removed",
            testInfo.getDisplayName()
        );
    }

    @Test
    void number1ShouldAlsoBeSupported2(TestInfo testInfo) {
        assertEquals(
            "number1 should also be supported2",
            testInfo.getDisplayName()
        );
    }
}