What characteristics should an effective modular test have?

An effective modular test should have the following characteristics:

• Isolation: the test checks only a small part of the code (module) without dependence on external systems.
• Repeatability: the test can be run multiple times with the same result.
• Automation: tests should run automatically without manual intervention.
• Speed: tests should execute quickly to not slow down the development process.
• Clarity: the test code should be simple and understandable to easily grasp what is being checked.
• Independence: the results of one test should not depend on other tests.

Example in Java using JUnit:

@Test
public void testAddition() {
    Calculator calc = new Calculator();
    int result = calc.add(2, 3);
    assertEquals(5, result);
}