[Junit-trackers] [ junit-Feature Requests-1550922 ] Assert should check types on Object

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Feature Requests item #1550922, was opened at 2006-09-02 04:20
Message generated for change (Comment added) made by dsaff
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Category: None
Group: None
>Status: Closed
>Resolution: Fixed
Priority: 5
Private: No
Submitted By: Jesse Glick (jglick)
Assigned to: Nobody/Anonymous (nobody)
Summary: Assert should check types on Object

Initial Comment:
org.junit.Assert.assertEquals should have a signature
such as

public static <T> void assertEquals(T expected, T actual);

rather than using (Object,Object). Similarly for the
variant taking a message, of course.

The additional typecheck would turn a dumb mistake such
as this:

List<String> names = ...;
...
assertEquals(Collections.singleton("foo"), names);
//                       ^^^^^^^^^
//                       should be: singletonList

into a compile-time error, rather than the cryptic test
failure message

expected:<[foo]> but was:<[foo]>

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>Comment By: David Saff (dsaff)
Date: 2009-11-18 15:31

Message:
Thanks, Jesse

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Comment By: Jesse Glick (jglick)
Date: 2009-11-16 18:20

Message:
commit de7ac4a1c3c7c9e59befe41d120daaa7827b7b24
Author: kbeck <kbeck>
Date:   Thu Feb 8 03:29:22 2007 +0000

    Added class names to error message when two values fail the equality
test but produce the same toString().


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Comment By: Jesse Glick (jglick)
Date: 2009-11-16 18:11

Message:
Seems JUnit 4.5 has already fixed this anyway:

    @Test public void compareTypes() {
        assertEquals(Collections.singleton(5), Arrays.asList(5));
    }

=>

expected: java.util.Collections$SingletonSet<[5]> but was:
java.util.Arrays$ArrayList<[5]>


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Comment By: David Saff (dsaff)
Date: 2009-11-16 12:52

Message:
This tracker is being shut down.  Please move this item to
http://github.com/KentBeck/junit/issues

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Comment By: Jesse Glick (jglick)
Date: 2006-09-06 11:02

Message:
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Sets and lists are not considered equal. The example should
have been corrected to e.g.

assertEquals(Collections.singleton("foo"), new
HashSet<String>(names));

I would like to see something like

expected: java.util.ArrayList <[foo]> but was:
java.util.Collections$SingletonSet <[foo]>

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Comment By: Matthias Schmidt (cmschmidt)
Date: 2006-09-06 10:48

Message:
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ARE a List and a Set not Comparable? Both are Collections
resp. Iterables. Depending on your program, you would either
have to compare their class types (1) or their content (2).
Both is possible.

1:
assertTrue( set.getClass() != list.getClass() );

2:
assertEquals(set.toArray(), list.toArray() );

Regarding your alternate strategy: I like the idea to
enhance the error message to something like "List <[]>
expected but was Set <[]>". Was it that what you meant?

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Comment By: Jesse Glick (jglick)
Date: 2006-09-06 09:55

Message:
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I meant to prevent a comparison between e.g. Set<String> and
List<String>. Unfortunately it seems javac will just treat
this as

<Object>assertEquals(..., ...);

which does not help anything. So it will not work.

Alternate strategy: in assertEquals, if the args are not
equal but their toString()s are equal, instead/additionally
print the impl class (o.getClass().getName()) of each. That
would at least clue you in to the fact that a List and a Set
are not comparable. I could supply a patch if you want one,
but it should be easy.

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Comment By: Matthias Schmidt (cmschmidt)
Date: 2006-09-04 07:52

Message:
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Are you sure there is a compile time error? I have rewritten
the assertEquals method as you suggested and written a test
like this:

@Test public void stringTest() {
  List<String> names = new ArrayList<String>();
  names.add("foo");
  assertEquals(Collections.singleton("foo"), names);
}

and the failure message was "expected:<[foo]> but
was:<[foo]>". So no real improvement here ;)

I am not sure if I understand what kind of typecheck you
would like to do. Is it to prevent to not be able to compare
e.g. a Boolean to an ArrayList?

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