Top 10 Negative Test Cases

Negative test cases are designed to test the software in ways it was not intended to be used, and should be a part of your testing effort. Below are the top 10 negative test cases you should consider when designing your test effort.

Top 10 Negative Test Cases ______________________________

1. Embedded Single Quote - Most SQL based database systems have issues when users store information that contain a single quote (e.g. John's car). For each screen that accepts alphanumeric data entry, try entering text that contains one or more single quotes. 

2. Required Data Entry - Your functional specification should clearly indicate fields that require data entry on screens. Test each field on the screen that has been indicated as being required to ensure it forces you to enter data in the field. 

3. Field Type Test - Your functional specification should clearly indicate fields that require specific data entry requirements (date fields, numeric fields, phone numbers, zip codes, etc). Test each field on the screen that has been indicated as having special types to ensure it forces you to enter data in the correct format based on the field type (numeric fields should not allow alphabetic or special characters, date fields should require a valid date, etc)

4. Field Size Test - Your functional specification should clearly indicate the number of characters you can enter into a field (for example, the first name must be 50 or less characters). Write test cases to ensure that you can only enter the specified number of characters. Preventing the user from entering more characters than is allowed is more elegant than giving an error message after they have already entered too many characters. 

5. Numeric Bounds Test - For numeric fields, it is important to test for lower and upper bounds. For example, if you are calculating interest charged to an account, you would never have a negative interest amount applied to an account that earns interest, therefore, you should try testing it with a negative number. Likewise, if your functional specification requires that a field be in a specific range (e.g. from 10 to 50), you should try entering 9 or 51, it should fail with a graceful message. 

6. Numeric Limits Test - Most database systems and programming languages allow numeric items to be identified as integers or long integers. Normally, an integer has a range of -32,767 to 32,767 and long integers can range from -2,147,483,648 to 2,147,483,647. For numeric data entry that do not have specified bounds limits, work with these limits to ensure that it does not get an numeric overflow error. 

7. Date Bounds Test - For date fields, it is important to test for lower and upper bounds. For example, if you are checking a birth date field, it is probably a good bet that the person's birth date is no older than 150 years ago. Likewise, their birth date should not be a date in the future. 

8. Date Validity - For date fields, it is important to ensure that invalid dates are not allowed (04/31/2007 is an invalid date). Your test cases should also check for leap years (every 4th and 400th year is a leap year). 

9. Web Session Testing - Many web applications rely on the browser session to keep track of the person logged in, settings for the application, etc. Most screens in a web application are not designed to be launched without first logging in. Create test cases to launch web pages within the application without first logging in. The web application should ensure it has a valid logged in session before rendering pages within the application. 

10. Performance Changes - As you release new versions of your product, you should have a set of performance tests that you run that identify the speed of your screens (screens that list information, screens that add/update/delete data, etc). Your test suite should include test cases that compare the prior release performance statistics to the current release. This can aid in identifying potential performance problems that will be manifested with code changes to the current release.

Globalization

Use Case Examples

Your use cases are only as good as the use someone's getting from them. What looks good to you may not be readable to your developers. The success measurement for an effective written use case is one that is easily understood, and ultimately the developers can build the right product the first time.

A great way for writing effective use cases is to walk through a simple use case example and watch how it can be leveraged to something complex. By absorbing the meaning of use case diagrams, alternate flows and basic flows, you will be able to apply use cases to your projects. In some of the tips below, we'll use eBay features for example use cases.

Tip 1. Be productive without perfection

Be agile, be lean, don't be afraid to make mistakes. Often so many new product managers think being perfect will impress their audience, but having strongly written use cases with a few mistakes is FAR better than an over complicated detailed list that confuses and bores an audience. 

When it comes to writing effective use cases, you don't need to be a perfectionist and concern yourself with getting it right the first time. Developing use cases should be looked at as an iterative process where you work and refine. You can always refine it later, so again, don't go for perfection from the get-go. Loosen up and have some fun while you're doing it. Remember, humans are reading your use cases, not a bunch of robots, so keep it interesting. 

Tip 2. Get a good working list of your use case actors

What is an actor? (no not Brad Pitt in this context) Any "object" or person that has behavior associated with it. Generally, the users are actors but often systems can be actors as well. 

There are possibly over a dozen actors that interact with Ebay, from buyers and sellers, down to suppliers, wholesalers, auditors, and customer service. But we're going for grass-roots, so who are the basic users of Ebay? BUYERS and SELLERS. So lets put them down as our first actors. (The visual notation in the figures below is based on UML -- Unified Markup Language for Use Cases) 

 

Do you notice how the actors aren't John and Sue which would be people? While John may be a seller and Sue may be a buyer, an actor is a Role. And a role in this case would be that of a buyer and that of a seller. Now that things are clicking, lets throw some more actors on your paper just so we can try and identify more possible users.

 

Now we have a bunch of actors. Wait a minute? Paypal? That's not a person. An actor can be a system, because a system plays another role in the context of your new system and has goals and interacts with other actors as you will see later. 

Tip 3. Define your Sunny Day Use Cases For those of you who haven't heard the expression, "Sunny Day" use cases, it is in reference to the use cases that are most likely going to occur when all goes well. These are somtimes referred to as your primary use cases. You always want to focus on the sunny day scenarios first because you can then pivot off these and figure out your "rainy day" scenarios (or edge cases) later.  Use the 80/20 rule -- if you write an exhaustive list of all possible use cases, typically 20% of the use cases will account for 80% of the activity. The other 80% of the use cases would support 20% of the activity. In my experience in various offices, the perfectionists will say, "well what about this? isn't that possible?" referring to an edge case. The product manager should be able to discern a common use case from the edge case and prioritize accordingly. So, once you are done with your sunny-day use cases, distribute it among your project team and get consensus that you have covered them all.  Now Collect your Rainy Day Use Cases After you have a well-defined list of your primary use cases, you'll want to collect the list of edge cases (rainy-day) and with the help of the product manager or stake-holder, prioritize them in terms of likelyness. It should be a business question as far as how much software development costs do you want to spend on something that is not likely to happen.

Tip 4. Identify reuse opportunity for use cases

In this step, you are going to cross the bridge into object modeling. Don't get overly concerned about terms like generalization, inheritance and extends. The goal of this Ebay use case example is to keep it understandable so we will explain this concept in terms of the example. 

What does the word general mean? Something is broad and not as detailed. Generalization is when you "inherit" from something general and then add more detail. A "person" is very general. A "man" is still general, but not as general as a "person". You can say that a "man" inherits behavior and atributes of a "person". 

Look at the requirements management use case diagram above and you will see there is duplicate behavior in both the buyer and seller which includes "create an account" and "search listings". Rather than have all of this duplication, we will have a more general user that has this behavior and then the actors will "inherit" this behavior from the new user. 

 

The above use case example diagram illustrates that a generic user creates accounts and search listings and that a buyer and a seller have their own behavior but also have the behavior of the generic user. The benefits of generalization are that you eliminate duplicate behavior and attributes that will ultimately make the system more understandable and flexible. We will see in later steps that this inheritance applies both to use cases and to the actors.

Tip 5. Create a use case index

After producing your initial visual list of use case actors and goals, we can take this list and create an initial use case grid which provides the basis for the use case index. Every use case will have various attributes relating both to the use case iteself and to the project. At the project level, these attributes include scope, complexity, status and priority. 

 

This use case index should be used by the project team to define the use cases against. It will serve as a master inventory to help writ effective use cases for the requirements phase of the project. 

Tip 6. Identify the key components of your use case

The actual use case is a textual representation illustrating a sequence of events. In our use case example, you will see that there are several components of a use case which we will review. In the mean time, review the table below to get a basic understanding of what is in the use case and then we will review each element as we progeress through our use case example.

Use Case Element	Description
Use Case Number	ID to represent your use case
Application	What system or application does this pertain to
Use Case Name	The name of your use case, keep it short and sweet
Use Case Description	Elaborate more on the name, in paragraph form.
Primary Actor	Who is the main actor that this use case represents
Precondition	What preconditions must be met before this use case can start
Trigger	What event triggers this use case
Basic Flow	The basic flow should be the events of the use case when everything is perfect; there are no errors, no exceptions. This is the "happy day scenario". The exceptions will be handled in the "Alternate Flows" section.
Alternate Flows	The most significant alternatives and exceptions

Tip 7. Name and briefly describe your use case

Now that you have a general understanding of what a use case consists of, we are ready to start creating our use case. Typically, while the name of your use case is being discussed, people will start briefly describing the use case. Use plain english and keep it simple. Getting back to our use case example, I will begin with use case #1 from step number four. 

Use Case Number:	1
Use Case Name:	Buyer Places a Bid
Description:	An EBAY buyer has identified an item they wish to buy, so they will place a bid for an item with the intent of winning the auction and paying for the item.

Tip 8. Create the use case basic flow

The basic flow of a use case represents the most important course of events or what happens most of the time, sometimes referred to as the 'Happy Day Scenario' because it is what occurs when everything goes well -- no errors or exceptions. Another reason why the basic flow is so critical is because it's much easier to fully comprehend the exceptions once the norm is understood and if the basic flow represents 70% of the system, the development staff is much more prone to implementing the correct code in the first pass.

For our use case example, the basic flow should be to describe the happy day scenario for your use cases such as "placing a bid". For a consumer to play a successful bid, what is the primary flow when everything goes as planned. An effective use cases needs to have the basic flow before moving forward with writing the alternate flows. 

Tip 9. Create the use case alternate flows

The basic flow is the key ingredient to your use case and some can argue that you can stop once you're done with the basic flow. It really depends on the level of detail you wish to achieve. However, providing more detail to the consumers of your use case is always a good thing. 

The alternate flows providing the following:

·         An exception or error flow to any line item in your basic flow

·         An additional flow, not necessarily error based, but a flow that COULD happen

A few examples of alternate flows are:

·         While a customer places an order, their credit card failed

·         While a customer places an order, their user session times out

·         While a customer uses an ATM machine, the machine runs out of receipts and needs to warn the customer

Tip 10. Produce your effective use case document

Recently at a new project assignment, I introduced a mid level developer to the concept of use cases which was totally foreign to him. Once walking him through the basic concepts and showing him the use case example, the lightbulb went off in his head on how convenient and simple it was to grasp the project.

A few reasons why it's that much easier to learn a system through use cases then a traditional requirements document is probably because with use cases, you are introduced to concepts at a high level, walk through a living scenario and then presented with specifications last. 

In several places in this document, I have stated "effective use cases" rather than just "use cases". The purpose of the use cases is for effective knowledge transfer from the domain expert to the software developer -- these use cases will serve as software requirements. If they don't make sense to the person building the software, they are not effective. There are several sources on the web for writing effective use cases including the book by Alistair Cockburn.

Tip 11. Generate a Use Case Model Diagram

You can use the Gatherspace.com use case modeling tool to produce a use case model within a few clicks. Once you define your use cases and actors, just go into the reporting section and click on the 'Use Case Model' report and that's it. From the main use case model, you can continue to drill down into the use cases.

To see what this looks like, click the use case model sample now. 

In several places in this document, I have stated "effective use cases" rather than just "use cases". The purpose of the use cases is for effective knowledge transfer from the domain expert to the software developer -- these use cases will serve as software requirements. If they don't make sense to the person building the software, they are not effective. There are several sources on the web for writing effective use cases including the book by Alistair Cockburn.

Tip 12. What's the difference between a User Story and a Use Case?

With so many engineering teams making the paradigm shift from waterfall to Agile Software Development, people often get caught up in having a pure Agile process which would include the use of User Stories. So what's all of the hoopla with User Stories? What are they, how are they different from use cases, do I need them, and where do they fit in the process? 

·         What is a User Story? Simply put, written from the context of the user as a simple statement about their feature need. They should generally have this format. "As a -role-, I want -goal/desire- so that -benefit-"

·         How is a User Story different than a Use Case? While a use case is highly structured and tells a story, the User Story sets the stage by stating the need. A User Story is the prelude to the use case by stating the need before the use case tells the story.

·         How does the User Story fit into the process? User Stories are great as an activity in collecting and prioritizing the high level features. Getting this initial feedback from the customer is a simple way of trying to get all of their needs identified and prioritized. The User Stories will then morph themselves into the business requirements and use cases.

Tip 13. In Agile Development, Keep Use Cases Agile, Mean and Lean

A common myth with Agile Development is that you *must* use user stories, and not use cases. Like anything else in life, nothing is black and white -- being Agile is really about smaller iterations, learning and adapting to the market.

If you are using Agile, Scrum and moving away from waterfall, what you want to do is make sure to iterate with your use cases. All that means is that your flows will be smaller and less feature rich. While the theme of the use case may appear the same from iteration to iteration, what is changing is the level of detail and the features inside the particular sprint. 

Creating a use case to long winded with too many features can potentially put a product at risk. What happens is that you can extend your release to market from two weeks to several months without the ability to learn from the iteration and adapt to the market. Keep those use cases learner! 

Defect Age

Defect Age can be measured in terms of any of the following:

• Time
• Phases

DEFECT AGE (IN TIME)

Definition

Defect Age (in Time) is the difference in time between the date a defect is detected and the current date (if the defect is still open) or the date the defect was fixed (if the defect is already fixed).

Elaboration

• The ‘defects’ are confirmed and assigned (not just reported).
• Dropped defects are not counted.
• The difference in time can be calculated in hours or in days.
• ‘fixed’ means that the defect is verified and closed; not just ‘completed’ by the developer.

Defect Age Formula

Defect Age in Time = Defect Fix Date (OR Current Date) – Defect Detection Date

Normally, average age of all defects is calculated.

Example

If a defect was detected on 01/01/2009 10:00:00 AM and closed on 01/04/2009 12:00:00 PM, the Defect Age is 74 hours.Uses

• For determining the responsiveness of the development/testing team. Lesser the age better the responsiveness.

DEFECT AGE (IN PHASES)

Definition

Defect Age (in Phases) is the difference in phases between the defect injection phase and the defect detection phase.

Elaboration

• ‘defect injection phase’ is the phase in the software life cycle where the defect was introduced.
• ‘defect detection phase’ is the phase in the software life cycle where the defect was identified.

Defect Age Formula

Defect Age in Phase = Defect Detection Phase – Defect Injection Phase

Normally, average of all defects is calculated.

Example

Let’s say the software life cycle has the following phases:

1. Requirements Development
2. High-Level Design
3. Detail Design
4. Coding
5. Unit Testing
6. Integration Testing
7. System Testing
8. Acceptance Testing

If a defect is identified in System Testing and the defect was introduced in Requirements Development, the Defect Age is 6.

Uses

• For assessing the effectiveness of each phase and any review/testing activities. Lesser the age better the effectiveness.

Testing techniques

The types of  Testing techniques fall in to 2 types.

• Static:
  - This type of testing techniques are applied before any test execution on any Software/Application.
  - This is also called as "Non-execution" technique.
  - Usually Static testing techniques is done in form of Documents with even source code, HLD/LLD documents, Functional specifications etc.
• Dynamic:
  - This type of testing technique is applied during the test execution on any Software/Application.

Lets see about Dynamic types of testing techniques.
Dynamic types of testing techniques is again sub-divided in to 3 types.

1. Structure-Based
2. Experience-Based
3. Specification-Based

The three specification based techniques are

1. Equivalence Class Partitioning
2. Boundary Value Analysis
3. Decision Table

1. Equivalence Class Partitioning [ECP]:
Testing cannot be done with all possible input conditions for validating any UI element, feature.

For example if a text box needs to tested whether is accepts from 1-60 characters, here testing is not possible with all numbers between 1 & 60. 

So, we can divide the range in to partitions, take one from each possible partition and test that particular text box.

• ECP is a specification based Black-box testing technique. 
• The intent of this technique is to divide the set of input conditions int to equal parts which are equal.
• Equivalence Partitions are also known as equivalence classes.
• This technique requires to take one input from each and if that not works we assume that any other input from that class does not work.

2. Boundary value analysis[BVA]:

In any application it is most likely common that error occurs at boundaries.

Boundary Value Analysis is also a specification based Black-box testing technique.  It is mainly based on testing the boundaries between the classes/partitions.

Boundary value is nothing but a edge value, that may be minimum or maximum value of a range.

Example; If a Text box accepts the range of 1-100 characters. Then the boundary values for this range would be   0,1,100,101.

Invalid          |      Valid   |    Invalid
  0                |1         100| 101

3. Decision Table:

In addition to the above both techniques which mainly focuses on the UI validation, Decision Table with all possible combinations focuses on the Logical values.

Decision Table is a type of Black-Box testing used to design the test cases with different combination of input's.
In this type of testing technique a table is designed with set of combinations and conditions.

Decision table looks like