How to refactor method?

How to refactor a method to make it easier to test

• Below is a method that I'm having a hard time figuring out how to test using JUnit. This method is difficult to test because it depends on the results of other methods (e.g. getClosestDcoumentCode). Based on my reading of JUnit, this suggests I should refactor the method. But how? And if refactoring is not necessary, how do you test a method that depends on other methods? Thank you, Elliott private static String findPrincipal(List<DocumentKey> documentkeys_) { Hashtable<String, Integer> codecounts = new Hashtable<String, Integer>(); for (DocumentKey document : documentkeys_) { int x = 0; String closestCode = getClosestDocumentCode(document.candidates); if (closestCode == null) continue; int thecount = 0; if (codecounts.containsKey(closestCode)) thecount = codecounts.get(closestCode); if (document.hasKey) thecount += 2; else thecount++; codecounts.put(closestCode, new Integer(thecount)); x++; } String closestCode = getClosestCode(codecounts); return closestCode; }

• Answer:

  It sounds to me like getClosestCode and getClosestDocumentCode belong to a different set of responsibilities than the findPrincipal method. So you'll want to begin by separating these into two different classes. Create an interface for each class to implement. The class that implements the findPrincipal method can then rely on the other interface as a constructor argument, like this: public class PrincipalFinderImpl implements PrincipalFinder { private CodeFinder codeFinder; public PrincipalFinderImpl(CodeFinder codeFinder) { this.codeFinder = codeFinder; } public String findPrincipal(List<DocumentKey> documentkeys_) { Hashtable<String, Integer> codecounts = new Hashtable<String, Integer>(); for (DocumentKey document : documentkeys_) { int x = 0; String closestCode = codeFinder.getClosestDocumentCode(document.candidates); if (closestCode == null) continue; int thecount = 0; if (codecounts.containsKey(closestCode)) thecount = codecounts.get(closestCode); if (document.hasKey) thecount += 2; else thecount++; codecounts.put(closestCode, new Integer(thecount)); x++; } String closestCode = codeFinder.getClosestCode(codecounts); return closestCode; } } Now it should be easy to create another class the implements the CodeFinder interface, either manually or using a Mocking framework. You can then control the results of each call to getClosestCode and getClosestDocumentCode, and ensure that each of these methods gets called with exactly the arguments you expect it to be called with.