Priority in TestNG

What is priority in TestNG?

The TestNG Priority is a mechanism used to force a specific execution order among test methods that belong to the same TestNG class. By default, TestNG does not guarantee any particular order for running test methods within a class; they might run in alphabetical order or another unpredictable sequence. Priority allows the developer to override this default behavior.

In TestNG, the priority attribute is used to define the order of execution of test methods in a class.

By default, TestNG executes test methods in alphabetical order of method names (not the order they appear in the code). If you want to control the execution order explicitly, you can assign a priority to each @Test method.

Key Points about `priority`:

The lower the priority number, the earlier the method will run.
priority = 0 will run before priority = 1, and so on.
If no priority is specified, TestNG assigns it a default priority of 0.
You can assign negative values as well.
If two or more tests have the same priority, they run in alphabetical order.

Example Java Code for Priority in TestNG

Below is the test class having multiple test methods having attribute priority in @Test annotation.

Output is shown below of the execution of test methods depends on priority values.

import org.testng.annotations.Test;

public class PriorityExample {

    @Test(priority = 1)
    public void testC() {
        System.out.println("Test C - Priority 1");
    }

    @Test(priority = 0)
    public void testA() {
        System.out.println("Test A - Priority 0");
    }

    @Test(priority = 2)
    public void testB() {
        System.out.println("Test B - Priority 2");
    }

    @Test  // No priority mentioned, default is 0
    public void testD() {
        System.out.println("Test D - Default Priority (0)");
    }
}

Output:

Test A - Priority 0
Test D - Default Priority (0)
Test C - Priority 1
Test B - Priority 2

Important points:

testA() and testD() both have priority 0. Since testA() comes alphabetically before testD(), it runs first.

Priorities help in defining explicit flow of tests, especially in dependent or staged testing scenarios.

In TestNG, when multiple test methods have the same priority, TestNG does not guarantee any specific execution order among them. It means that the methods with the same priority may be executed in any order, and this order can change across different runs.

Lower priority value = executed earlier

Same priority value = no guaranteed order among those methods

Example Code: Same Priority Test Methods

Below in test class, first three test methods have same priority that 1, last method has priority as 0.
Below is the output shown the execution flow of all test methods. Please have a look.

import org.testng.annotations.Test;

public class SamePriorityExample {

    @Test(priority = 1)
    public void testA() {
        System.out.println("Test A - Priority 1");
    }

    @Test(priority = 1)
    public void testB() {
        System.out.println("Test B - Priority 1");
    }

    @Test(priority = 1)
    public void testC() {
        System.out.println("Test C - Priority 1");
    }

    @Test(priority = 0)
    public void testD() {
        System.out.println("Test D - Priority 0");
    }
}

Output:

Test D - Priority 0
Test A - Priority 1
Test B - Priority 1
Test C - Priority 1

Another Run Might Give:

Test D - Priority 0
Test C - Priority 1
Test A - Priority 1
Test B - Priority 1

If multiple test methods share the same priority, TestNG may run them in any order. So, do not rely on order of execution if you assign the same priority to multiple test methods.