How do you handle since Unit test is not very accurate ?

[tangara goh]

Dear experts,

I am running into another puzzle which I hope to know how to handle.

So here's the test I am trying to run :

public static void testSort(){

String[] input = {"I", "am", "an", "apple"};

String[] expected = {"I", "am", "an", "apple"};

Sort.sort(input);

if(input! = expected){
System.out.println("Errror! There seems to be a problem");

So, when you run the test, it will actually shows the System.out.println("Error! There seems to be a problem");

How do you handle this kind of situation, especially for beginner like me, since they are not supposed to print that line since input did == expected.

[Stephan van Hulst]

Attach a debugger to your test and step through the code until you find the line that is incorrect.

If you do so, you will find that input != expected. Why? Well, what does the != operator mean for arrays?

[Tim Holloway]

If you use the jUnit testing framework it does this sort of stuff for you.

Instead of "if" statements and "println"s, jUnit has a set of assert methods that can be used to test, throw an Exception on failure, and report the offending values.

[tangara goh]

Stephan van Hulst wrote:Attach a debugger to your test and step through the code until you find the line that is incorrect.

If you do so, you will find that input != expected. Why? Well, what does the != operator mean for arrays?

But, I find this fake "passed" can be very dangerous to people who are ignorant about it.

Therefore, I find JUnit itself is not 100% reliable....

[Tim Holloway]

tangara goh wrote:
Therefore, I find JUnit itself is not 100% reliable....

I'm not following that. If I code an "assertEquals( a_test_array, testedObject.getArray() )" method call, I'd expect that thanks to the wonders of polymorphism (and/or introspection) that jUnit would be able to do an element-by-element verification of an array.

On the other hand, "a_test_array != testedObject.getArray()" would almost invariably return true, because to be otherwise would require both arguments to be the exact same instance of an array, and not merely that the tested object's array has the proper values in it.

[Rob Spoor]

Tim Holloway wrote:If I code an "assertEquals( a_test_array, testedObject.getArray() )" method call, I'd expect that thanks to the wonders of polymorphism (and/or introspection) that jUnit would be able to do an element-by-element verification of an array.

Unfortunately you'd be wrong. JUnit has separate assertArrayEquals methods for comparing arrays element by element. assertEquals is not overloaded to take arrays.

[Tim Holloway]

It's probably better that waym since you can thus compare for equality or identity, whichever your need,

Regardless of the method name, though the assertion does exist, though, so to say jUnit doesn't handle it accurately doesn't make sense.

[Stephan van Hulst]

tangara goh wrote:But, I find this fake "passed" can be very dangerous to people who are ignorant about it.

What fake "passed"? You want to see if the contents of two arrays are equal right? Then just don't use the != operator, because it doesn't compare array contents.

Therefore, I find JUnit itself is not 100% reliable....

Like Tim, I really don't understand what you mean by this. JUnit is fine, and should be your first choice for writing unit tests.

If your tests are unreliable, that's your fault, not JUnit's.

[Liutauras Vilda]

tangara goh wrote:But, I find this fake "passed" can be very dangerous to people who are ignorant about it.

Therefore, I find JUnit itself is not 100% reliable....

As been said already, it did what you asked it for. There might be well cases where you really want to check whether compared references are exact same instances, although much rarer.

There are tools which can advice you along the way about such developer mistakes. Such tools might be SonarCube/SonarCloud or simply an IDE extension as SonarLint, which would highlight it for you asking to verify your intention.