16. Solution: Custom ClassLoader

Solution: Custom ClassLoader

TestRunner.java

import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.List;

public final class TestRunner {

  public static void main(String[] args) throws Exception {
    if (args.length != 2) {
      System.out.println("Usage: TestRunner [test folder] [test name]");
      return;
    }
    List<String> passed = new ArrayList<>();
    List<String> failed = new ArrayList<>();
    Class<?> testClass = getTestClass(args[0], args[1]);
    for (Method method : testClass.getDeclaredMethods()) {
      if (method.getAnnotation(Test.class) == null) {
        continue;
      }
      try {
        UnitTest test = (UnitTest) testClass.getConstructor().newInstance();
        test.beforeEachTest();
        method.invoke(test);
        test.afterEachTest();
        passed.add(getTestName(testClass, method));
      } catch (Throwable throwable) {
        failed.add(getTestName(testClass, method));
      }
    }

    System.out.println("Passed tests: " + passed);
    System.out.println("FAILED tests: " + failed);
  }

  private static Class<?> getTestClass(String testFolder, String className) throws Exception {
    URL testDir = Path.of(testFolder).toUri().toURL();
    URLClassLoader loader = new URLClassLoader(new URL[]{testDir});
    Class<?> klass = Class.forName(className, true, loader);
    if (!UnitTest.class.isAssignableFrom(klass)) {
      throw new IllegalArgumentException("Class " + klass.toString() + " must implement UnitTest");
    }
    return klass;
  }

  private static String getTestName(Class<?> klass, Method method) {
    return klass.getName() + "#" + method.getName();
  }
}