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Interdependence of unit tests

Since recently, I am trying out unit testing to get acquainted with the practice, and to ultimately write better code. I have started on one of my big projects, with a rather large untested code base, but am only unit testing utility classes, that don't have many dependencies and are quite easy to test.
I have read quite a bit of introductory material to unit testing in general, and what often comes up is that unit tests should always test the smallest possible unit of behaviour. That is to say, that whether a test passes or fails should only depend on a very specific piece of code, such as a small method.
However, I am already finding problems to put this idea into practice. Consider for example :
#Test
public void testSomethingWithFoo() {
Foo foo = new Foo(5);
Bar result = foo.bar(); //Suppose this returns new Bar(42) for some reason.
Bar expected = new Bar(42);
Assert.assertEquals(expected, result); // Implicitly calls Bar.equals, which returns true if both Bars' constructor parameters are equal.
}
Clearly, this test depends on two elements : the foo.bar() method, but also the bar.equals(otherBar) method, which is implicitly called by the assertion.
Now, I could write an other test, which asserts that this bar.equals() method works correctly. However, say it fails. Now, my first test also should fail, but for a reason beyond its scope.
My point is that, for this particular example, nothing really is problematic; I could maybe check for equality without using equals at all. However, I feel like this sort of issue will become a real problem with more complex behaviours, where avoiding existing methods because they might not work would involve rewriting large amounts of code just for tests.
How to translate these requirements into code, without making unit tests interdependent ?
Is it even possible ? If not, should I stop bothering about this issue, and assume all methods not under the current test work ?

However, say it fails. Now, my first test also should fail, but for a
reason beyond its scope.
Test isolation is a really important thing, you are right but note also that this has a limitation.
You will necessary fall into some cases where in your unit tests, you will have to rely on other general methods of other objects such as equals/hashCode or still constructors.
This is unavoidable. Sometimes, the coupling is not an issue.
For example, using a constructor to create the object passed to the method under test or a mock value is natural and should really not be avoided !
But in other cases, the coupling with the API of another class is not desirable.
It is for example the case in your sample code as your test relies on an equals() method which the fields tested may change through the time and also be functionally different from fields to watch/assert in the tested method.
In addition, this doesn't make the fields asserted explicit.
In this kind of case, to assert fields values of a returned object by the method under test, you should assert field by field via getter methods.
To avoid writing this repetitive and error prone code, I use a matcher testing library such as AssertJ or Hamcrest (included in JUnit at a time) that provides fluent and flexible way to assert the content of an instance.
For example with AssertJ :
Foo foo = new Foo(5);
Bar actualBar = foo.bar();
Assertions.assertThat(actualBar)
.extracting(Bar::getId) // supposing 42 is stored in id field
.containsExactly(42);
With such a simple example, matcher testing library has no real value. You could directly do :
Foo foo = new Foo(5);
Bar actualBar = foo.bar();
Assert.assertEquals(42, actualBar.getId())
But for cases where you want to check multiple fields (very common case), it is very helpful :
Foo foo = new Foo(5);
Bar actualBar = foo.bar();
Assertions.assertThat(actualBar)
.extracting(Bar::getId, Bar::getName, Bar::getType)
.containsExactly(42, "foo", "foo-type);

I've found it helpful to divide my classes into two main types:
Types which hold data. They represent your data's structure, and contain little to no logic.
Types which hold logic, and hold no state.
The reason for this is that many classes at many layers will inevitably be tied to your data model, so you want the representation of your data model to be rock solid and unlikely to yield any surprises.
If Bar is a data structure, then relying on the behavior of its .equals() method isn't much different than relying on the behavior of int or String's .equals() behavior. You should stop worrying about it.
On the other hand, if Bar is a logic class, you probably shouldn't be relying on its behavior at all when you're trying to test Foo. In fact, Foo shouldn't be creating a Bar at all (unless Foo is a BarFactory, e.g.). Instead, it should be relying on interfaces which can be mocked.
When it comes to testing your Data types (especially in the exceptional cases where the data type really needs to have some logic, like a Uri class, you will of a necessity be testing multiple methods within that class (like Bar's constructor and equals method). But the tests should all be testing that class specifically. Make sure you've got plenty of tests to keep these rock-solid.
When testing a service class (one with logic), you will effectively be assuming that any data types you're dealing with have been tested sufficiently so you're really testing the behavior of the type you're worried about (Foo) and not the other types you happen to be interacting with (Bar).

Junit of equals method

I just want to know if there is a best practice or a common way to test equals implementation in objects. I mean test method that has been overridden.
public boolean equals(Object o)
I did using some logic like this. (Suppose number and name need to be equals to obtain true)
Dog d1 = new Dog(1,"Alvin");
Dog d2 = new Dog(2,"Alvin");
Assert.assertFalse(d1.equals(null));
Assert.assertFalse(d1.equals(d2));
d2.setId(1);
d2.setName("Kelvin");
Assert.assertFalse(d1.equals(d2));
d2.setName("Alvin");
Assert.assertTrue(d1.equals(d2));
Assert.assertTrue(d1.equals(d1));
But when there are a lot of fields this task is very large and boring, so my question is if there is any framework, tool, option, anything that makes this easier and can proof that method has been overridden correctly. thanks.
I know that override the method equals depends on the logic that you need, but also test case creation is, so looking for an standard way to test the method avoiding large codes in test cases, if there is exists obviously or any suggestion you might have.

Looking in the link of the duplicate question I read #user598656 answer and suggest to use MeanBeans (Automated java bean tester)
Reading the documentation I found this feature.
5.2.7. Property!Significance!Test!Algorithm!
The property significance test algorithm is as follows:
for each property in public getter/setter method pairs do
create instance of class under test, object x
create instance of class under test, object y
change property of y to contain a different value
if property is insignificant then
assert x.equals(y)
else
assert x.equals(y) is false
end if
end for
It is what I was looking for, the answer is the last one but in my opinion this fit my needs.

You can use field based templates of Fast code ecllipse plugin .You can write a simple template and select many fields you want, from a class, to generate the statements using those fields.

Generics - Create data on the fly

This is a complicated question which i will find hard to explain so i appologise in advance.
Imagine an application that invokes another projects methods. I need a way of generating data to match the parameter list. Obviously if the parameter types are of some class that I have no way of generating then it should fail but if its an int[] and int[][] a List<String> a Map<Integer, String> then it should be possible.
What i am struggling with is a decent approach for solving this. I can get the types of parameters via method.getGenericParameterTypes(); example for the parameter HashMap would be java.util.HashMap<java.lang.String, java.lang.Integer> but there are quite a lot of different possibilities right!
I assume generics has some use here? The only issue with that being I have no control over the code that is being invoked. How can I use one of these types and then generate data for it?
I am sorry for the poor explanation, any help appreciated
Thanks
Here we see an example of a method i want to invoke, I want to record how long it takes to run (this is being done via reflection) however, i need to generate data for the parameters. I need a way of generating data to match
public void someMethod(Param a, Param b, Param c)
{
//some user code I have no control over
}

I think perhaps the question should be why you need to do this. Perhaps if you explained your use/business case, we can provide a cleaner (and easier) solution.
From your very last lines, you are talking about wanting to profile the method. Generally speaking, it is rare to want to profile just one small tiny method in the middle of chain of processing. That being said, I can imagine some convoluted cases where this might occur. However, even at that, it should be a handful of cases that you would be able to code yourself.
If it is a question of actual profiling, but you are not sure how to do it, and consequently feel that the only way is to call each method individually so you can "wrap" it with a start/stop timer, I would strongly recommend looking into AOP. Both Spring and AspectJ are great for AOP, with AspectJ able to do byte-weaving that Spring is unable to accomplish.
Consequently, with AspectJ you would be able to create your own profiling timer classes and weave them into the byte-code at compile time and then run your standard tests, but visualize all the profiling info that you want/need on a per-method basis.
And best of all, it would avoid you needing to come up with some convoluted scheme for producing random test data that isn't really relevant to the method being tested.

Sounds like a horrible problem.
If you have the class[] that represents the parameter types of the method then can't you create a new instance of each and pass that as the arguments list to the method? This is untested:
Class[] parameterTypes = method.getGenericParameterTypes();
Object[] args = new Object[parameterTypes.length];
for (int i=0; i < parameterTypes.length; i++) {
args[i] = parameterTypes[i].newInstance(); // assuming the classes can be instantiated without params
}
method.invoke(obj, args); // I assume you've instantiated the object already

How to test for equality of complex object graphs?

Say I have a unit test that wants to compare two complex for objects for equality. The objects contains many other deeply nested objects. All of the objects' classes have correctly defined equals() methods.
This isn't difficult:
#Test
public void objectEquality() {
Object o1 = ...
Object o2 = ...
assertEquals(o1, o2);
}
Trouble is, if the objects are not equal, all you get is a fail, with no indication of which part of the object graph didn't match. Debugging this can be painful and frustrating.
My current approach is to make sure everything implements toString(), and then compare for equality like this:
assertEquals(o1.toString(), o2.toString());
This makes it easier to track down test failures, since IDEs like Eclipse have a special visual comparator for displaying string differences in failed tests. Essentially, the object graphs are represented textually, so you can see where the difference is. As long as toString() is well written, it works great.
It's all a bit clumsy, though. Sometimes you want to design toString() for other purposes, like logging, maybe you only want to render some of the objects fields rather than all of them, or maybe toString() isn't defined at all, and so on.
I'm looking for ideas for a better way of comparing complex object graphs. Any thoughts?

The Atlassian Developer Blog had a few articles on this very same subject, and how the Hamcrest library can make debugging this kind of test failure very very simple:
How Hamcrest Can Save Your Soul (part 1)
Hamcrest saves your soul - Now with less suffering! (part 2)
Basically, for an assertion like this:
assertThat(lukesFirstLightsaber, is(equalTo(maceWindusLightsaber)));
Hamcrest will give you back the output like this (in which only the fields that are different are shown):
Expected: is {singleBladed is true, color is PURPLE, hilt is {...}}
but: is {color is GREEN}

What you could do is render each object to XML using XStream, and then use XMLUnit to perform a comparison on the XML. If they differ, then you'll get the contextual information (in the form of an XPath, IIRC) telling you where the objects differ.
e.g. from the XMLUnit doc:
Comparing test xml to control xml [different]
Expected element tag name 'uuid' but was 'localId' -
comparing <uuid...> at /msg[1]/uuid[1] to <localId...> at /msg[1]/localId[1]
Note the XPath indicating the location of the differing elements.
Probably not fast, but that may not be an issue for unit tests.

Because of the way I tend to design complex objects, I have a very easy solution here.
When designing a complex object for which I need to write an equals method (and therefore a hashCode method), I tend to write a string renderer, and use the String class equals and hashCode methods.
The renderer, of course, is not toString: it doesn't really have to be easy for humans to read, and includes all and only the values I need to compare, and by habit I put them in the order which controls the way I'd want them to sort; none of which is necessarily true of the toString method.
Naturally, I cache this rendered string (and the hashCode value as well). It's normally private, but leaving the cached string package-private would let you see it from your unit tests.
Incidentally, this isn't always what I end up with in delivered systems, of course - if performance testing shows that this method is too slow, I'm prepared to replace it, but that's a rare case. So far, it's only happened once, in a system in which mutable objects were being rapidly changed and frequently compared.
The reason I do this is that writing a good hashCode isn't trivial, and requires testing(*), while making use of the one in String avoids the testing.
(* Consider that step 3 in Josh Bloch's recipe for writing a good hashCode method is to test it to make sure that "equal" objects have equal hashCode values, and making sure that you've covered all possible variations are covered isn't trivial in itself. More subtle and even harder to test well is distribution)

The code for this problem exists at http://code.google.com/p/deep-equals/
Use DeepEquals.deepEquals(a, b) to compare two Java objects for semantic equality. This will compare the objects using any custom equals() methods they may have (if they have an equals() method implemented other than Object.equals()). If not, this method will then proceed to compare the objects field by field, recursively. As each field is encountered, it will attempt to use the derived equals() if it exists, otherwise it will continue to recurse further.
This method will work on a cyclic Object graph like this: A->B->C->A. It has cycle detection so ANY two objects can be compared, and it will never enter into an endless loop.
Use DeepEquals.hashCode(obj) to compute a hashCode() for any object. Like deepEquals(), it will attempt to call the hashCode() method if a custom hashCode() method (below Object.hashCode()) is implemented, otherwise it will compute the hashCode field by field, recursively (Deep). Also like deepEquals(), this method will handle Object graphs with cycles. For example, A->B->C->A. In this case, hashCode(A) == hashCode(B) == hashCode(C). DeepEquals.deepHashCode() has cycle detection and therefore will work on ANY object graph.

Unit tests should have well-defined, single thing they test. This means that in the end you should have well-defined, single thing that can be different about those two object. If there are too many things that can differ, I would suggest splitting this test into several smaller tests.

I followed the same track you are on. I also had additionnal troubles:
we can't modify classes (for equals or toString) that we don't own (JDK), arrays etc.
equality is sometimes different in various contexts
For example, tracking entities equality might rely on database ids when available ("same row" concept), rely the equality of some fields (the business key) (for unsaved objects). For Junit assertion, you might want all fields equality.
So I ended up creating objects that run through a graph, doing their job as they go.
There is typically a superclass Crawling object:
crawl through all properties of the objects ; stop at:
enums,
framework classes (if applicable),
at unloaded proxies or distant connections,
at objects already visited (to avoid looping)
at Many-To-One relationship, if they indicate a parent (usually not included in the equals semantic)
...
configurable so that it can stop at some point (stop completely, or stop crawling inside the current property):
when mustStopCurrent() or mustStopCompletely() methods return true,
when encountering some annotations on a getter or a class,
when the current (class, getter) belong to a list of exceptions
...
From that Crawling superclass, subclasses are made for many needs:
For creating a debug string (calling toString as needed, with special cases for Collections and arrays that don't have a nice toString ; handling a size limit, and much more).
For creating several Equalizers (as said before, for Entities using ids, for all fields, or solely based on equals ;). These equalizers often need special cases also (for example for classes outside your control).
Back to the question : These Equalizers could remember the path to the differing values, that would be very useful your JUnit case to understand the difference.
For creating Orderers. For example, saving entities need to be done is a specific order, and efficiency will dictate that saving the same classes together will give a huge boost.
For collecting a set of objects that can be found at various levels in the graph. Looping on the result of the Collector is then very easy.
As a complement, I must say that, except for entities where performance is a real concern, I did choose that technology to implements toString(), hashCode(), equals() and compareTo() on my entities.
For example, if a business key on one or more fields is defined in Hibernate via a #UniqueConstraint on the class, let's pretend that all my entities have a getIdent() property implemented in a common superclass.
My entities superclass has a default implementation of these 4 methods that relies on this knowledge, for example (nulls need to be taken care of):
toString() prints "myClass(key1=value1, key2=value2)"
hashCode() is "value1.hashCode() ^ value2.hashCode()"
equals() is "value1.equals(other.value1) && value2.equals(other.value2)"
compareTo() is combine the comparison of the class, value1 and value2.
For entities where performance is of concern, I simply override these methods to not use reflexion. I can test in regression JUnit tests that the two implementations behave identically.

We use a library called junitx to test the equals contract on all of our "common" objects:
http://www.extreme-java.de/junitx/
The only way I can think of to test the different parts of your equals() method is to break down the information into something more granular. If you are testing a deeply-nested tree of objects, what you are doing is not truly a unit test. You need to test the equals() contract on each individual object in the graph with a separate test case for that type of object. You can use stub objects with a simplistic equals() implementation for the class-typed fields on the object under test.
HTH

I would not use the toString() because as you say, it is usually more useful for creating a nice representation of the object for display or logging purposes.
It sounds to me that your "unit" test is not isolating the unit under test. If, for example, your object graph is A-->B-->C and you are testing A, your unit test for A should not care that the equals() method in C is working. Your unit test for C would make sure it works.
So I would test the following in the test for A's equals() method:
- compare two A objects that have identical B's, in both directions, e.g. a1.equals(a2) and a2.equals(a1).
- compare two A objects that have different B's, in both directions
By doing it this way, with a JUnit assert for each comparison, you will know where the failure is.
Obviously if your class has more children that are part of determining equality, you would need to test many more combinations. What I'm trying to get at though is that your unit test should not care about the behavior of anything beyond the classes it has direct contact with. In my example, that means, you would assume C.equals() works correctly.
One wrinkle may be if you are comparing collections. In that case I would use a utility for comparing collections, such as commons-collections CollectionUtils.isEqualCollection(). Of course, only for collections in your unit under test.

If you're willing to have your tests written in scala you could use matchete. It is a collection of matchers that can be used with JUnit and provide amongst other things the ability to compare objects graphs:
case class Person(name: String, age: Int, address: Address)
case class Address(street: String)
Person("john",12, Address("rue de la paix")) must_== Person("john",12,Address("rue du bourg"))
Will produce the following error message
org.junit.ComparisonFailure: Person(john,12,Address(street)) is not equal to Person(john,12,Address(different street))
Got : address.street = 'rue de la paix'
Expected : address.street = 'rue du bourg'
As you can see here I've been using case classes, which are recognized by matchete in order to dive into the object graph.
This is done through a type-class called Diffable. I'm not going to discuss type-classes here, so let's say that it is the corner stone for this mechanism, which compare 2 instances of a given type. Types that are not case-classes (so basically all types in Java) get a default Diffable that uses equals. This isn't very useful, unless you provide a Diffable for your particular type:
// your java object
public class Person {
public String name;
public Address address;
}
// you scala test code
implicit val personDiffable : Diffable[Person] = Diffable.forFields(_.name,_.address)
// there you go you can now compare two person exactly the way you did it
// with the case classes
So we've seen that matchete works well with a java code base. As a matter of fact I've been using matchete at my last job on a large Java project.
Disclaimer : i'm the matchete author :)

Java equals(): to reflect or not to reflect

This question is specifically related to overriding the equals() method for objects with a large number of fields. First off, let me say that this large object cannot be broken down into multiple components without violating OO principles, so telling me "no class should have more than x fields" won't help.
Moving on, the problem came to fruition when I forgot to check one of the fields for equality. Therefore, my equals method was incorrect. Then I thought to use reflection:
--code removed because it was too distracting--
The purpose of this post isn't necessarily to refactor the code (this isn't even the code I am using), but instead to get input on whether or not this is a good idea.
Pros:
If a new field is added, it is automatically included
The method is much more terse than 30 if statements
Cons:
If a new field is added, it is automatically included, sometimes this is undesirable
Performance: This has to be slower, I don't feel the need to break out a profiler
Whitelisting certain fields to ignore in the comparison is a little ugly
Any thoughts?

If you did want to whitelist for performance reasons, consider using an annotation to indicate which fields to compare. Also, this implementation won't work if your fields don't have good implementations for equals().
P.S. If you go this route for equals(), don't forget to do something similar for hashCode().
P.P.S. I trust you already considered HashCodeBuilder and EqualsBuilder.

Use Eclipse, FFS!
Delete the hashCode and equals methods you have.
Right click on the file.
Select Source->Generate hashcode and equals...
Done! No more worries about reflection.
Repeat for each field added, you just use the outline view to delete your two methods, and then let Eclipse autogenerate them.

If you do go the reflection approach, EqualsBuilder is still your friend:
public boolean equals(Object obj) {
return EqualsBuilder.reflectionEquals(this, obj);
}

Here's a thought if you're worried about:
1/ Forgetting to update your big series of if-statements for checking equality when you add/remove a field.
2/ The performance of doing this in the equals() method.
Try the following:
a/ Revert back to using the long sequence of if-statements in your equals() method.
b/ Have a single function which contains a list of the fields (in a String array) and which will check that list against reality (i.e., the reflected fields). It will throw an exception if they don't match.
c/ In your constructor for this object, have a synchronized run-once call to this function (similar to a singleton pattern). In other words, if this is the first object constructed by this class, call the checking function described in (b) above.
The exception will make it immediately obvious when you run your program if you haven't updated your if-statements to match the reflected fields; then you fix the if-statements and update the field list from (b) above.
Subsequent construction of objects will not do this check and your equals() method will run at it's maximum possible speed.
Try as I might, I haven't been able to find any real problems with this approach (greater minds may exist on StackOverflow) - there's an extra condition check on each object construction for the run-once behaviour but that seems fairly minor.
If you try hard enough, you could still get your if-statements out of step with your field-list and reflected fields but the exception will ensure your field list matches the reflected fields and you just make sure you update the if-statements and field list at the same time.

You can always annotate the fields you do/do not want in your equals method, that should be a straightforward and simple change to it.
Performance is obviously related to how often the object is actually compared, but a lot of frameworks use hash maps, so your equals may be being used more than you think.
Also, speaking of hash maps, you have the same issue with the hashCode method.
Finally, do you really need to compare all of the fields for equality?

You have a few bugs in your code.
You cannot assume that this and obj are the same class. Indeed, it's explicitly allowed for obj to be any other class. You could start with if ( ! obj instanceof myClass ) return false; however this is still not correct because obj could be a subclass of this with additional fields that might matter.
You have to support null values for obj with a simple if ( obj == null ) return false;
You can't treat null and empty string as equal. Instead treat null specially. Simplest way here is to start by comparing Field.get(obj) == Field.get(this). If they are both equal or both happen to point to the same object, this is fast. (Note: This is also an optimization, which you need since this is a slow routine.) If this fails, you can use the fast if ( Field.get(obj) == null || Field.get(this) == null ) return false; to handle cases where exactly one is null. Finally you can use the usual equals().
You're not using foundMismatch
I agree with Hank that [HashCodeBuilder][1] and [EqualsBuilder][2] is a better way to go. It's easy to maintain, not a lot of boilerplate code, and you avoid all these issues.

You could use Annotations to exclude fields from the check
e.g.
#IgnoreEquals
String fieldThatShouldNotBeCompared;
And then of course you check the presence of the annotation in your generic equals method.

If you have access to the names of the fields, why don't you make it a standard that fields you don't want to include always start with "local" or "nochk" or something like that.
Then you blacklist all fields that begin with this (code is not so ugly then).
I don't doubt it's a little slower. You need to decide whether you want to swap ease-of-updates against execution speed.

Take a look at org.apache.commons.EqualsBuilder:
http://commons.apache.org/proper/commons-lang/javadocs/api-3.2/org/apache/commons/lang3/builder/EqualsBuilder.html