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How to define priority in JUnit5

I have some unit test built with Junit in a Java project.
The only issue is that I want to define the order/priority of the tests.
I mean... I'm using #BeforeAll to execute first test, which is the login process and to get the access for the postlogin functionalities.
But right after that, I want to run another specific test.
And then the rest...
I checked and there is an option to use #Order() annotation, but my idea is not to be ordering every test like this... I just wanna run first the login, and then a test that I need to run all the others. So after the first two test, the others doesn't matter in which order they are.

First, having unit tests depend on other unit tests is typically bad design. The JUnit 5 User Guide mentions this:
Although true unit tests typically should not rely on the order in which they are executed, there are times when it is necessary to enforce a specific test method execution order — for example, when writing integration tests or functional tests where the sequence of the tests is important, especially in conjunction with #TestInstance(Lifecycle.PER_CLASS).
Consider if what you're doing is testing or set-up. If the action of logging in is just set-up for your tests then you should do this in a method annotated with #BeforeAll or #BeforeEach, whichever makes more sense in your context. Afterwards, you may need to clean-up using #AfterAll or #AfterEach, depending on which "before annotation" you used.
If you're actually trying to test the login code then try to separate these tests from the others. You could do this by moving them into a separate class file or even leveraging #Nested classes (if appropriate). Instead of having your later tests require a real login you should use a fake login. In other words, mock the dependencies needed for the later tests. This will remove the inter-test dependency situation. And don't be afraid to re-"login" for each test (e.g. by using #BeforeEach); if you're using mocks this shouldn't be too expensive.
Note: As of JUnit 5.4 you might even be able to abort some tests if previous tests fail using a TestWatcher extension, as mentioned in this Q&A. However, using such an approach seems better suited for integration tests rather than unit tests.
That said, what you want should be possible. You mention #Order but then say you're hesitant to use it because you don't want to order every method, only make sure that two tests run before all the others. You don't have to add the annotation to every method. If you look at the documentation of MethodOrderer.OrderAnnotation, you'll see:
MethodOrderer that sorts methods based on the #Order annotation.
Any methods that are assigned the same order value will be sorted arbitrarily adjacent to each other.
Any methods not annotated with #Order will be assigned a default order value of Integer.MAX_VALUE which will effectively cause them to appear at the end of the sorted list.
And from Order.value():
Elements are ordered based on priority where a lower value has greater priority than a higher value. For example, Integer.MAX_VALUE has the lowest priority.
This means you only need to annotate your two tests with #Order and leave the rest alone. All the test methods without the #Order annotation will run in any order, but after the first two tests.
#TestMethodOrder(MethodOrderer.OrderAnnotation.class)
class MyTests {
#Test
#Order(1)
void firstTest() {}
#Test
#Order(2)
void secondTest() {}
#Test
void testFoo() {}
#Test
void testBar() {}
// other tests...
}

Does using Method Interceptor in TestNG skips the test on fail or Execute it even if any fails?

I would like to know if using this answer skips the following test methods or marks it as fails. I know if priority is used the following methods will be run and will not be dependent. I wanna know how method interceptor orders the methods....
Thanks...

I believe what you're asking is: When using an IMethodInterceptor to order tests, will a failed test method cause subsequent tests to fail? No. Ordering tests using IMethodInterceptor does not create dependencies.
This is pretty easy to test yourself. I definitely recommend trying it out to see how it behaves in different scenarios.

How to make JUnit test cases to run in sequential order?

I am using JUnit4.
I have a set of test methods in a test case.
Each test method inserts some records and verify a test result and finally delete the records inserted.
Since the JUnit run in parallel, test methods fail because of some
records present during the execution of previous test method. This
happen only in my colleague machine(Windows 7), not in my machine(Cent
OS 6).
What we need is that the test methods have to pass in all our machines.
I have tried clearing the records in the Setup() method but again it works only on my machine. Is there any option available in JUnit to make the test methods to run in a uniform sequential order ?
Thanks,

MethodSorters is a new class introduced after Junit 4.6 release. This class declared three types of execution order, which can be used in your test cases while executing them.
NAME_ASCENDING(MethodSorters.NAME_ASCENDING) - Sorts the test methods
by the method name, in lexicographic order.
JVM(null) - Leaves the test methods in the order returned by the
JVM. Note that the order from the JVM my vary from run to run.
DEFAULT(MethodSorter.DEFAULT) - Sorts the test methods in a
deterministic, but not predictable, order.
.
import org.junit.FixMethodOrder;
import org.junit.Test;
import org.junit.runners.MethodSorters;
//Running test cases in order of method names in ascending order
#FixMethodOrder(MethodSorters.NAME_ASCENDING)
public class OrderedTestCasesExecution {
#Test
public void secondTest() {
System.out.println("Executing second test");
}
#Test
public void firstTest() {
System.out.println("Executing first test");
}
#Test
public void thirdTest() {
System.out.println("Executing third test");
}
}
Output:
Executing first test
Executing second test
Executing third test
Reference: http://howtodoinjava.com/2012/11/24/ordered-testcases-execution-in-junit-4/

JUnit 4.11 now supports specifying execution order using #FixMethodOrder annotation.

Ordering of tests is not guaranteed in JUnit.
The reason for this is that unit tests are meant to be atomic - all of the setup should happen in the setup / tear down methods, but not by other tests.
Consider moving the code that inserts data into another helper class that can be called by both the test that's inserting and the class that needs to verify, and calling that class in your #Before methods.
You should also consider a mocking solution (eg Mockito) as opposed to hitting the database directly if you can - mocking will go a long way to ensuring that your tests are nice and isolated, and, as a nice side benefit, usually help point out where you could use some refactoring.

Because you're running the tests in parallel, and you're hitting the database, you're highly likely to have problems, because the database won't necessarily be in a coherent state for each test.
Solution: don't run your tests in parallel. JUnit doesn't run the tests in parallel by default, so either you're setting the option in maven or using one of the parallel runners in JUnit.
If you're still having problems between tests failing on Windows but not on Cent OS, then it's maybe a problem with run order, which you'll need to fix. See my answer to Has JUnit4 begun supporting ordering of test? Is it intentional?.
The way around this (at least in JUnit terms) is to remove the dependencies between tests. Basically, JUnit doesn't support ordering and the tests should be able to be run in any order.
If you really need to have dependencies between tests, use TestNG, where you can have dependencies.

There is no problem running tests in parallel even if you have your data layer in it. But you need to have additional work to create MOCK UPs for your data so not it will not hit the database. You can use different mockup frameworks like Mockito, EasyMock and Arquillian.

How to pre-define the running sequences of junit test cases？

I have a test class in java and there are several methods annotated by #Test in it, somehow, i want to Junit run method A before method B when i run the whole tests. Is it possible or necessary?

This sort of dependency on test methods is bad design and should be avoided. If there is initialization code in one test method that needs to be done for the next, it should be factored out into a setUp method.

The problem I have with this is reporting. If you WANT/NEED to see if each test method fails or passes then you're SCREWED.
I understand that you don't want one test to build upon previous tests, But regardless of that, there may be situations that you need it to do this (or you'll increase the complexity of the test by an order of magnitude).
Should the flow of tests in the code be up to the developer of the tests or the developer of the framework ?
Show JUnit test code to 10 java developers, and I'll be willing to bet most will assume that the tests (regardless of anything external) will be run in the order they appear in the test class.
Shouldn't THAT be the default behaviour of JUnit ? (Give me the option of telling it the order instead of JUnit figuring it out" on its own.)
Update: 2014-11-18
The newer version of JUnit supports method sorters
// This saves the tests in alphabetical order
#FixMethodOrder(MethodSorters.NAME_ASCENDING)
I would think that you might be able to create your own method sorter if you "really" wanted do do your own specific order.

Tests should have independent order, but some times we have not what we want.
If you have a large legacy project with thousands of tests, and they depends on their execution order, you will have many problems, when, for example you will try to migrate on java 7, because it will shuffle all tests.
You can read more about this problem here:
junit test ordering and java 7

If it's only two methods then you'd need to wrap it in a single unit test that truly isn't order-dependent.
#Test
public void testInOrder() throws Exception {
testA();
testB();
}

use the following to setup thing before and after tests
#Before
public void setUp() throws MWException {
}
#After
public void tearDown() {
}

How can I run (or change the order of) specific test-methods in a JUnit test class?

I am fairly new to Java. I have constructed a single JUnit test class and inside this file are a number of test methods. When I run this class (in NetBeans) it runs each test method in the class in order.
Question 1: How can I run only a specific sub-set of the test methods in this class?
(Potential answer: Write #Ignore above #Test for the tests I wish to ignore. However, if I want to indicate which test methods I want to run rather than those I want to ignore, is there a more convenient way of doing this?)
Question 2: Is there an easy way to change the order in which the various test methods are run?
Thanks.

You should read about TestSuite's. They allow to group & order your unit test methods. Here's an extract form this article
"JUnit test classes can be rolled up
to run in a specific order by creating
a Test Suite.
EDIT: Here's an example showing how simple it is:
public static Test suite() {
TestSuite suite = new TestSuite("Sample Tests");
suite.addTest(new SampleTest("testmethod3"));
suite.addTest(new SampleTest("testmethod5"));
return suite;
}

This answer tells you how to do it. Randomizing the order the tests run is a good idea!
Like the comment from dom farr states, each unit test should be able to run in isolation. There should be no residuals and no given requirements after or before a test run. All your unit tests should pass run in any order, or any subset.
It's not a terrible idea to have or generate a map of Test Case --> List of Test and then randomly execute all the tests.

There are a number of approaches to this, but it depends on your specific needs. For example, you could split up each of your test methods into separate test classes, and then arrange them in different test suites (which would allow for overlap of methods in the suites if desired). Or, a simpler solution would be to make your test methods normal class methods with one test method in your class that calls them in your specific order. Do you want them to be dynamcially called?

I've not been using Java that long either, but as far as I've seen there isn't a convenient method of marking methods to execute rather than ignore. Instead I think this could be achieved using the IDE. When I want to do that in Eclipse I can use the junit view to run individual tests by clicking on them. I imagine there is something similar in Netbeans.
I don't know of an easy way to reorder the test execution. Eclipse has a button to rerun tests with the failing tests first, but it sounds like you want something more versatile.