Assertions in Java are used to validate the program’s assumptions at runtime. They help identify and diagnose potential defects in the code. When an assertion fails, an exception is thrown, indicating that the program is in an unexpected state.

To use assertions in Java, the assert keyword is used followed by a boolean expression that represents the expected condition. If the condition evaluates to false, an AssertionError is thrown. Here’s an example:

int x = 5;
assert x > 0 : "x should be positive";

In this example, if the value of x is not greater than 0, the assertion will fail, and an AssertionError with the message “x should be positive” will be thrown.

One important thing to note is that assertions are disabled by default in Java. To enable them, you need to run the JVM with the -ea or -enableassertions flag. For example:

java -ea MyClass

Test Assertions

Test assertions are used in unit testing frameworks to verify expected behavior in your code. They are similar to assertions but are specifically used within test cases. Test assertions provide a mechanism to compare actual results with expected results and report any discrepancies.

Java provides several test assertion methods in the Assert class, such as assertEquals, assertTrue, assertFalse, etc. These methods are commonly used in testing frameworks like JUnit and TestNG.

Here’s an example using JUnit:

import org.junit.Assert;
import org.junit.Test;

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

In this example, the assertEquals method is used to compare the expected result of 5 with the actual result of the addition operation. If the values don’t match, the test will fail.

By using test assertions in your unit tests, you can ensure that your code behaves as expected and identify any potential bugs or issues.

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