15 minutes to read

Role of testing in the Waterfall and Agile methodologies of software development

April 9, 2021

Software testing has proved to be an essential part of the software development process. Still, it plays different roles in various software development methodologies, and as a result, it is executed in different ways. We'd like to throw light on the most widely spread software development methodologies, i.e. Agile and Waterfall. So let's get it started.

The Waterfall methodology

The Waterfall methodology is a sequential model of software development. Therefore, all SDLC phases - requirements analysis, software design, software development, software testing, software deployment, and software maintenance - are performed one after another, without being overlapped or modified after completion. So QA engineers can proceed to the active QA process only after accomplishment of the development phase. As a result, in Waterfall projects, testing is executed through a single cycle.

The prominent feature of the Waterfall methodology is comprehensive, sometimes even excessive documentation. Indeed, a lot of attention is paid to project/business requirements and planning. This has either pros or cons. On the one hand, developers and QA engineers have at their disposal well-thought-out and detailed requirements that clearly describe the way a product should work. On the flip side, it is rather time-incentive and may considerably postpone product development taking into account the fact that the development phase cannot begin if work on the previous phases has not been finished yet. Besides, it is impossible to check project requirements for ambiguities and inconsistencies from the get-go as a QA team joins to work when it is its turn.

Another prominent feature of this methodology is strict adherence to a predetermined plan, as a result, there is no opportunity to update project or business requirements and change a road map.

Advantages of the Waterfall methodology

Well-defined and properly documented processes;

It is much easier to control a Waterfall project as every phase has accurately defined outcomes and a strict review process;

There is no need for frequent meetings and continuous communication. QA experts and development teams work independently;

Due to scrupulous compliance with predetermined goals and plans, it is rather easy to define required resources and budget;

As long as there is no room for any changes, there are good chances to meet the stated budget and time limits;

Shifting teams can easily adapt.

Disadvantages of the Waterfall methodology

A need for excessive documentation;

Intolerance to any changes in project requirements;

This methodology is not appropriate for large-scale projects;

The Waterfall methodology loses its effectiveness in case predefined outcomes and requirements are not clear;

A QA team gets into gear just upon the accomplishment of the development phase as a result, bugs pile up and their fixing can be fairly expensive and difficult;

A working product can be presented only after the development phase has been finished; it can result in serious risks and unexpected outcomes.

When to use the Waterfall methodology

The Waterfall methodology has merits and flaws. As a result, to get the most out of it, you should know when it makes sense to implement this software development model:

Straightforward, small-scale, and medium-sized projects with clear and stable requirements;

Projects, usually government ones, for which close supervision and accurately defined budget, and time frames play an important role;

Projects that must comply with numerous rules and norms (e.g. healthcare software).

The Agile methodology

The Agile methodology a well-known incremental software development model. For this reason, testing is executed throughout the whole SDLC. Besides, development and testing activities are carried out simultaneously in Agile projects. Therefore, the main merit of the methodology is the capability to reveal defects and fix them as early as possible.

The Agile model suggests close collaboration within a product team and with a customer. As a rule, stakeholders revise the product state after every iteration and reconsider task priority for the succeeding iteration to assure product compliance with market requirements and business objectives.

Frequent releases are a distinctive feature of Agile. This attitude gives teams an opportunity to improve software continuously. Due to easy debugging, openness to changes, and fast updates, Agile teams can hit a market with a great product that meets users' needs and expectations.

In contrast to the Waterfall methodology, not so much time is spent on requirements and planning and more emphasis is given to customer feedback It is also worth mentioning that a lack of detailed plan and constant changes make it almost impossible to properly define resources and budget needed to implement a project.

The core principles of the Agile methodology:

Members of teams and communication over tools and processes;

Working product over excessive documentation;

Focus on customer's needs over contract terms;

Openness to changes over strict adherence to a plan;

Numerous teams have already highly appreciated the numerous benefits of Agile, and this methodology is currently gaining momentum. It has a few flavors, the most famous of them are Kanban, Scrum, and XP standing for;

Extreme Programming.

Advantages of the Agile methodology

Minimal preliminary planning is needed;

Minimal documentation is needed;

Intensive communication helps product team members and stakeholders be on the same page, avoid possible misunderstandings, and reveal weak spots of a project;

Working product or its prototype can be presented as quickly as possible;

As software testing is conducted for every iteration, bugs don't pile up;

The Agile model is rather flexible as it gives an opportunity to address frequent changes and consequently deliver a product that complies with the market demands;

The customer's needs are of primary importance for the Agile methodology.

Disadvantages of the Agile methodology

In spite of numerous merits, the Agile methodology is not perfect as well and has some drawbacks. Let's take a look at them:

Agile projects require close communication and collaboration; as a result, plenty of time is spent on numerous meetings. In essence, daily meetings are a norm for Agile projects;

Vague organizational structure;

The methodology is ineffective for small-scale projects;

It is fairly difficult to properly define the needed resources and budget from the outset;

If a customer has a vague vision of a project, its development can easily get taken off track;

Inconsistent documentation or its absence makes it difficult for newcomers to hit the ground running.

When to use the Agile methodology

To be able to achieve excellent results, it is important to know when the Agile methodology is appropriate and can bring a lot of benefits. Let's consider some common cases:

Any startup, when it is unclear whether a product will be well accepted on the market and users' feedback is required from the very beginning;

Medium-sized projects with vague business and project requirements;

Large-scale projects that can be split into smaller parts to be developed separately.

The Agile methodology versus the Waterfall methodology

You may have already noticed that the two methodologies under consideration are worlds apart in their attitude to software development and software testing. That is why let's sum up the information and take a closer look at the main differences presented in the table below.

The Waterfall methodology	The Agile methodology
The methodology has sequential nature. Thus, testing is executed through a single cycle.	The methodology has iterative nature. Therefore, testing is executed through several cycles.
Testing is deemed to be an independent phase of SDLC and conducted as soon as the development phase has been accomplished.	Testing is not considered to be a separate activity and performed simultaneously with software development.
Comprehensive documentation and long-range planning are needed.	Minimal documentation is needed and a short-range plan is drawn up.
The emphasis is on the contract terms and prepared plan of activities.	The emphasis is on the customer's business objectives and users' needs.
The required resources and budget can be accurately estimated.	It is almost impossible to properly define the required resources and budget in advance.
The customer is not so actively engaged and there is no need for frequent communication.	Close collaboration and customer engagement are required throughout the whole development process.
The rigid development process, SDLC phases cannot be overlapped.	The flexible development process SDLC phases can be overlapped.
Any changes are restricted.	Changes are welcomed.
A working product can be presented only at the end of the development process.	A working product can be presented in the shortest possible time and then its functionality is continuously enriched with each iteration.
The Waterfall methodology implies rare releases.	The Agile methodology implies frequent releases.

Bottom line

Both software development methodologies Waterfall and Agile stand apart from the rest. They are the most widely used due to the pleiad of the benefits they offer. However, the Agile model is getting more popular as most projects tend to undergo numerous changes in order to meet fast-changing market conditions. Still, the Waterfall model is a viable option for projects with stable requirements and those that demand strict control and adherence to plan. Now, knowing all peculiarities of each methodology you can choose the one that perfectly matches your project.