1. ## Boundary Values

Here is a sample exam question for which I disagree with the answer, which one is correct?

An input field takes the year of birth between 1900 and 2004.
The boundary values for testing this field are

a) 1899, 1900, 2004,2005
b) 0 ,1900,2004, 2005
c) 1899, 1900, 1901, 2003, 2004, 2005
d) 1900, 2004

I think it's c but the quiz said it's A. Why is my answer incorrect?

2. ## Re: Boundary Values

In c) 1900, 1901, 2003, 2004 could all be considered "between 1900 and 2004", while 1899 and 2005 could be considered "not between 1900 and 2004".

3. ## Re: Boundary Values

Because 1901 &amp; 2003 (in answer C) fall into a valid partition they must be valid boundaries. They are also at the edge of a partition. This is why I still think C is the correct answer.

4. ## Re: Boundary Values

1899 &amp; 2005 are in both answers. So that doesn't answer my question.

5. ## Re: Boundary Values

What are the boundaries being tested? Is a value that is within an equivalent class part of a boundary test?

6. ## Re: Boundary Values

[ QUOTE ]
Because 1901 &amp; 2003 (in answer C) fall into a valid partition they must be valid boundaries. They are also at the edge of a partition. This is why I still think C is the correct answer.

[/ QUOTE ]
No.

The (hidden) assumption in the phrase "An input field takes the year of birth between 1900 and 2004" is that the endpoint dates are "inclusive" - that is, they are inside the valid partition.

So the only "edge" here is 1900 is "inside" and 1899 is "outside". 2004 is "inside" and 2005 is "outside". 1901 and 2003 are no more important to the set of boundary values than 1902, 1903, 2001, 2002, etc.

This is something that is easily confirmed by a discussion, but is impossible to confirm in a multiple-choice exam.

7. ## Re: Boundary Values

Actually both A and C are correct. What practice test did you get this question from? It is a poor question.

A is called the two-point boundary value set, where each boundary consists of 2 points: one invalid and one valid.

C is called the three-point boundary value set. It is derived mathematically [ (X-1) &lt; X &lt; (X+1) ]. I believe the theory comes from Boris Beizer. It claims that X is the boundary, and the other 2 values are on the boundary and should be tested.

A is what the Foundation level teaches as the boundary theory. Most advanced test analyst courses teach both A and C.

For my money, A is preferable; I have never seen an extra defect detected using the three-point method.

8. ## Re: Boundary Values

Jamiemi has got this spot on, the correct answer is either A or C, it depends upon whether or not 2 value boundary value analysis method is selected or the 3 value approach.

Which one to use will depend upon how important or how critical the system is. The bigger the risk, then go for the 3 value approach. Less riskier apps select the 2 value approach.

Whether to use the 2 or 3 value approach, this should be clearly defined in the Test Strategy or Test Plan docs

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