What is an edge case? Meaning, examples in software development

Chat with any product manager or product owner working on a complex product and you’ll discover that edge cases are one of the major challenges they encounter when building new products or features.

Often, product managers shoulder the full blame for failing to identify edge cases early in the product development process — that is, before the sprint begins.

So, what is an edge case? Why is acknowledging, identifying, and prioritizing them crucial? How can they impact your product’s user experience?

What is an edge case?

An edge case is a rare and unexpected use case or user scenario that ventures outside the boundaries envisaged by the product manager and developers. These scenarios are often overlooked during the early stages of writing the product requirements document (PRD) and user stories because they don’t align with normal or expected product usage.

Edge cases are marked by their departure from usual patterns and can reveal vulnerabilities or unexpected behaviors in a product. These nuances might not become apparent during standard testing or development.

Why do edge cases occur?

Edge cases happen for various reasons. Here are, in my view, some of the top causes that I’ve experienced:

• Unpredictable user behavior — Users interact with products in diverse and unpredictable ways, leading to edge cases that might not have been anticipated during product development
• Diverse user environments — Users utilize products under various conditions, with differing hardware configurations and network conditions, generating scenarios that can provoke edge cases
• Incomplete requirements (PRDs, user stories, specifications) — Some edge case scenarios may be overlooked or not fully contemplated during the analysis phase before the sprint, leading to unforeseen behaviors in real-world situations
• Product complexity — As products evolve to become more complex and interconnected, the interactions between different components may give rise to unanticipated edge cases that are challenging for the product manager and the technical team to identify
• Data variability — Real-world data can display exceptional patterns or outliers that must be thoroughly accounted for in the product’s design.
• External factors — Changes in regulations, technology upgrades, or unexpected events are external factors that can influence edge cases, impacting the product’s behavior
• Resource constraints — In situations with limited resources such as memory, processing power, or bandwidth, edge cases can surface when the product is pushed to its limits
• Interoperability issues — Compatibility issues may prompt edge case scenarios when products need to interact with other systems or devices.
• Human error — User errors or mistakes, either intentional or unintentional, can also result in edge cases
• Evolution of use cases — As the product evolves or ventures into new markets and regions, unforeseen edge cases may arise due to changing user needs and expectations
• Limited test coverage — Sometimes, due to time constraints, the technical team plans for limited test coverage. This can lead to edge cases as these indirect user scenarios won’t be covered by the testing team

Examples of edge cases

To gain a better understanding of what edge cases look like in the real world, let’s explore some hypothetical examples:

• Currency conversion rounding issue — A finance app inaccurately handles rounding errors when converting currencies, resulting in incorrect calculations for certain amounts
• Emoji handling in text fields — A messaging app crashes when a user attempts to send a message containing a seldom-used or complex emoji or symbol
• Battery saver mode impact — A mobile game significantly depletes the device’s battery when played in battery saver mode, leading to negative user feedback
• Time zone mismatch — A scheduling software erroneously displays events in the wrong time zone when users cross international date lines, causing confusion and missed appointments
• Long usernames and layout distortion — A social media platform’s user interface malfunctions and displays incorrectly when someone with an exceptionally long username interacts with it
• Extremely slow internet connection — An online shopping app fails to load product images correctly for users on incredibly slow internet connections, resulting in a frustrating shopping experience
• Accessibility in voice assistant — A voice-activated home device does not respond accurately to users with specific accents or speech patterns, making it difficult for them to use the device effectively
• Uncommon file format support — A document processing software unexpectedly crashes when trying to open rarely used file formats, leading to data loss and inconvenience for users
• Special characters in passwords — In a password management app, the product requirements document covers strong password requirements but neglects the scenario where certain special characters are not allowed. This oversight leads to login issues for users with such characters in their passwords

Practical steps to identify edge cases

As you can see, identifying edge cases early in — or, preferably, before — the product development lifecycle is paramount to ensuring a smooth user experience. Here are five practical steps to help you spot edge cases before they lead to unexpected issues in your product:

1. Thorough requirements gathering
2. Well-prepared product requirements documents (PRDs)
3. Scenario-based testing
4. Iterative development
5. Beta testing with diverse users

1. Thorough requirements gathering

Conduct in-depth discussions with stakeholders and users to pinpoint potential edge cases. Ensure they are included in the product requirements. Organize product review sessions to comb through your PRDs and gather valuable feedback from all stakeholders.

2. Well-prepared product requirements documents (PRDs)

Before forwarding your requirements to the engineers and adding them to the sprint, take your time. Ensure they are reviewed by your engineers. Include your quality engineers/software testers and leverage their analytical skills to identify minor user scenarios. Be certain to use their capabilities to the fullest to identify these cases.

3. Scenario-based testing

Collaborate closely with the quality engineers to design test cases that cover a broad range of scenarios, including edge cases. This is to validate the product’s behavior under various conditions. Work with them to ideate and brainstorm all test cases.

4. Iterative development

There’s no need to cover all edge cases from the outset. Adopt an iterative development approach to incorporate lessons learned from previous releases and improve the product’s resilience over time.

Collaborate with your engineers to prioritize and scope the newly discovered edge cases, addressing them in the upcoming sprints so as not to disrupt the process.

5. Beta testing with diverse users

Involve a diverse group of beta testers to simulate real-world scenarios and collect feedback on any encountered edge cases.

Key takeaways

Edge cases may appear less significant in the early stages of product development, but they can lead to significant problems down the line if not identified and addressed. The key to mastering edge cases lies in maintaining a balanced perspective that values the typical user scenarios while not overlooking the outliers.

Embrace the challenges presented by edge cases. Collaborating closely with your development team to identify them will enable you to create impeccable products that leave a lasting impression on your users.

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