Junit assertCollection?

Posted on 2011-03-14
Last Modified: 2012-05-11
What's the best way to unit test that 2 collections are the same.
(Not the same object, but each element value of one collection is in the other, and vice versa)
Question by:allelopath
  • 4
LVL 47

Expert Comment

ID: 35132060

Are all objects in your collections unique?
Or you may have two equal options present in any of your two collections?

if they are unique then if the sizes of both collections are equal,
and then you just traverse one collection and check that
all elements of this coll;ection are present in the second collection then
tyour collections are the same in the sense you mentioned
LVL 47

Expert Comment

ID: 35132107

if my question above has the anser "yes" then this method should work:

boolean areTheyEqual(ArrayList a1, ArrayList a2){
if(a1.size() != a2.size() ) return false;

for(int j=0; j<a1.size(); j++){
return false;
return true;


LVL 47

Accepted Solution

for_yan earned 500 total points
ID: 35132225

I think this should work even if each collection
has identical items:

boolean areTheyEqual(ArrayList a1, ArrayList a2){
if(a1.size() != a2.size() ) return false;
for(int j =0; j<a1.size(); j++){
int count1 = 0;
for(int k=0; k<a1.size(); k++){

int count2 = 0;
for(int k=0; k<a2.size(); k++){

if(count1 != count2)return false;

retrurn true;

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Author Comment

ID: 35132239
Looks like I could also use Apache Commons CollectionsUtils
CollectionUtils.isEqualCollection(actual, expected);
LVL 47

Expert Comment

ID: 35132266
Yes, you are right - that probably would be better.
But it is nice to invent the wheel also :)
LVL 86

Expert Comment

ID: 35132479
boolean identical = coll1.size() == 0;

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