Best way to automagically migrate tests from JUnit 3 to JUnit 4?

Here are the actual regular expressions I used to execute furtelwart's suggestions:

// Add @Test
Replace:
^[ \t]+(public +void +test)
With:
    @Test\n    $1
Regular Expression: on
Case sensitive: on
File name filter:
*Test.java

// Remove double @Test's on already @Test annotated files
Replace:
^[ \t]+@Test\n[ \t]+@Test
With:
    @Test
Regular Expression: on
Case sensitive: on
File name filter:
*Test.java


// Remove all empty setUp's
Replace:
^[ \*]+((public|protected) +)?void +setUp\(\)[^\{]*\{\s*(super\.setUp\(\);)?\s*\}\n([ \t]*\n)?
With nothing
Regular Expression: on
Case sensitive: on
File name filter:
*Test.java

// Add @Before to all setUp's
Replace:
^([ \t]+@Override\n)?[ \t]+((public|protected) +)?(void +setUp\(\))
With:
    @Before\n    public void setUp()
Regular Expression: on
Case sensitive: on
File name filter:
*Test.java

// Remove double @Before's on already @Before annotated files
Replace:
^[ \t]+@Before\n[ \t]+@Before
With:
    @Before
Regular Expression: on
Case sensitive: on
File name filter:
*Test.java


// Remove all empty tearDown's
Replace:
^[ \*]+((public|protected) +)?void +tearDown\(\)[^\{]*\{\s*(super\.tearDown\(\);)?\s*\}\n([ \t]*\n)?
With nothing
Regular Expression: on
Case sensitive: on
File name filter:
*Test.java

// Add @After to all tearDown's
Replace:
^([ \t]+@Override\n)?[ \t]+((public|protected) +)?(void +tearDown\(\))
With:
    @After\n    public void tearDown()
Regular Expression: on
Case sensitive: on
File name filter:
*Test.java

// Remove double @After's on already @After annotated files
Replace:
^[ \t]+@After\n[ \t]+@After
With:
    @After
Regular Expression: on
Case sensitive: on
File name filter:
*Test.java


// Remove old imports, add new imports
Replace:
^([ \t]*import[ \t]+junit\.framework\.Assert;\n)?[ \t]*import[ \t]+junit\.framework\.TestCase;
With:
import org.junit.After;\nimport org.junit.Before;\nimport org.junit.Test;\nimport static org.junit.Assert.*;
Regular Expression: on
Case sensitive: on
File name filter:
*Test.java


// Remove all extends TestCase
Replace:
[ \t]+extends[ \t]+TestCase[ \t]+\{
With:
 {
Regular Expression: on
Case sensitive: on
File name filter:
*Test.java



// Look for import junit.framework;
Find:
import junit\.framework
Manually fix
Regular Expression: on
Case sensitive: on


// Look for ignored tests (FIXME, disabled, ...)
Find:
public[ \t]+void[ \t]+\w+test
Manually fix
Regular Expression: on
Case sensitive: on


// Look for dummy/empty tests
Find:
public[ \t]+void[ \t]+test[\w\d]*\(\s*\)\s*\{\s*(//[^\n]*)?\s*\}
Manually fix
Regular Expression: on
Case sensitive: on

Note: it's important to do them in the order shown above.

In my opinion, it cannot be that hard. So let's try it:

0. Imports

You need to import three annotations:

import org.junit.After;
import org.junit.Before;
import org.junit.Test;`

After you've made the next few changes, you won't need import junit.framework.TestCase;.

1. Annotate test* Methods

All methods beginning with public void test must be preceded by the @Test annotation. This task is easy with a regex.

2. Annotate SetUp and TearDown methods

Eclipse generates following setUp() method:

@Override
protected void setUp() throws Exception { }

Must be replaced by:

@Before
public void setUp() throws Exception { }

Same for tearDown():

@Override
protected void tearDown() throws Exception { }

replaced by

@After
public void tearDown() throws Exception { }

3. Get rid of extends TestCase

Remove exactly one occurence per file of the string

" extends TestCase"

4. Remove main methods?

Probably it's necessary to remove/refactor existing main methods that will execute the test.

5. Convert suite() method to @RunWithClass

According to saua's comment, there must be a conversion of the suite() method. Thanks, saua!

@RunWith(Suite.class)
@Suite.SuiteClasses({
  TestDog.class
  TestCat.class
  TestAardvark.class
})

Conclusion

I think, it's done very easy via a set of regular expressions, even if it will kill my brain ;)

We are in the middle of migrating a reasonably large code base to JUnit4. Since this is the second time I'm doing a migration such as this, I decided to save the code somewhere:

https://github.com/FranciscoBorges/junit3ToJunit4

It deals with more corner cases than the ones enumerated in answers above. Such as:

• calls to TestCase.setUp() and TestCase.tearDown()
• calls to TestCase(String) constructor within a sub-class constructor
• calls to TestCase.assert* methods that moved to Assert.
• fixing package names junit.framework to org.junit
• etc