Eclipse: Flip arguments using regular expressions

Lately I have migrated a project from JUnit to TestNG. With the help of an Ecplipse plugin this is a one-click task. Every assert-method is replaced by its counterpart in class org.testng.AssertJUnit. This is only an intermediate solution. The final goal is to use org.testng.Assert. This will present a small challenge. JUnit’s two arg assert-methods, e.g. assertEquals or assertSame define order expected, actual. TestNG defines the opposite. Therefore argument order needs to be flipped.

Flipping argument order is achived with the help of Find/Replace and regular expressions. To find all assertEquals-methods and flip their arguments, follow 5 steps:

1. Within the respective test class call the Find/Replace-dialog, either via menu entry Edit or via [Strg]-F.
2. Check Regular expressions.
3. Enter assertEquals\(([^,]+),\s*([^)]+)\s*\) into text field Find.
4. Enter assertEquals(\2, \1) into text field Replace.
5. Click button Replace All.

The regular expression in text field Find makes use of two capturing groups. Capturing groups are created with ([^,]+) and ([^)]+). They are referenced in text field Replace in reverse order with \2 and \1.