What are the common pitfalls of Java function testing?

Common pitfalls that you should be aware of when unit testing Java functions include: Ignoring boundary conditions such as empty inputs, maximum or minimum values. Input is assumed to be valid and invalid input is not validated. Piling was not performed when relying on third-party libraries, resulting in unstable testing. Forget about testing exceptions that functions may throw.

Common traps in Java function testing

When unit testing Java functions, you need to pay special attention to some common traps, which may cause the test to fail. Comprehensive or unreliable.

1. Ignore boundary conditions

Boundary condition testing refers to testing the behavior of the input and output of a function under extreme values. Forgetting to test boundary conditions, such as empty inputs, maximum or minimum values, can lead to undiscovered defects.

Practical case:

@Test
public void testMax() {
    assertTrue(Math.max(2, 5) == 5);
}

This test does not cover the case where the Math.max function is used with negative numbers or 0 as input . A more comprehensive test would look like this:

@Test
public void testMax() {
    assertTrue(Math.max(2, 5) == 5);
    assertTrue(Math.max(0, -5) == 0);
}

2. Assume the input is valid

The test should not assume that the input is always valid. Developers should consider the possibility of invalid input and validate input if necessary.

Practical case:

@Test
public void testSqrt() {
    assertTrue(Math.sqrt(4) == 2.0);
}

This test does not consider the situation where Math.sqrt accepts negative input, which will result in IllegalArgumentException. A more robust test should look like the following:

@Test
public void testSqrt() {
    assertTrue(Math.sqrt(4) == 2.0);
    try {
        Math.sqrt(-4);
        fail("Expected IllegalArgumentException");
    } catch (IllegalArgumentException e) {}
}

3. No stubbing when relying on third-party libraries

When the test function depends on a third-party library, if stubbing is not performed, it may Causing test failure or instability. Stubbing allows simulating the behavior of third-party libraries to control the test environment.

Practical case:

@Test
public void testSendMail() {
    assertTrue(MailSender.sendMail("to@example.com", "subject", "body"));
}

This test does not stub the MailSender class, so the test relies on the actual behavior of sending emails. This can cause tests to fail, or cause flakiness if the email fails to be sent.

4. Forget to test for exceptions

Functions can throw exceptions, and forgetting to test for these exceptions can lead to errors or incomplete test coverage.

Practical case:

@Test
public void testDivide() {
    assertTrue(Divider.divide(10, 2) == 5);
}

This test does not test the Divider class thrown when the input is 0 #ArithmeticException. A more comprehensive test would look like this:

@Test
public void testDivide() {
    assertTrue(Divider.divide(10, 2) == 5);
    try {
        Divider.divide(10, 0);
        fail("Expected ArithmeticException");
    } catch (ArithmeticException e) {}
}

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