What are some common assertions provided by TestNG?

In software testing, assertions are a crucial technique used to verify whether the code's behavior meets the expected outcome. TestNG is a testing framework for the Java programming language, providing a rich set of assertion capabilities to help testers effectively inspect and validate test results. The following are some common assertion methods in TestNG:

1. assertEquals: This is the most commonly used assertion for verifying whether two values or objects are equal. For example, if you expect a function to return 10, you can use assertEquals(10, result) to validate.

2. assertNotEquals: Opposite to assertEquals, this assertion confirms that two values or objects are not equal. For instance, to verify that an error scenario does not return the expected value.

3. assertTrue and assertFalse: These assertions are used for checking boolean values. If you want to verify a condition is true or false, these assertions are highly applicable. For example, assertTrue(isUserLoggedIn) can be used to confirm whether a user is logged in.

4. assertNull and assertNotNull: These assertions are used to check if an object is null. For example, assertNotNull(user) can confirm that the user object is not null.

5. assertSame and assertNotSame: These methods are used to check whether two object references point to the same object or different objects. assertSame(expectedObject, actualObject) is used to verify whether two references point to the same memory address.

6. assertThrows: This assertion is available for Java 8 and later versions and is used to confirm that the expected exception is thrown. This is useful for verifying exception handling.

For example, suppose we are testing a user registration feature. We need to confirm that when a user provides an existing email, the system throws a UserAlreadyExistsException exception. We can use assertThrows(UserAlreadyExistsException.class, () -> userService.register(user)) to validate this.

Through these assertions, TestNG provides powerful tools to help developers and testers ensure that the code meets business requirements and functional expectations.