The Tool Desk
Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →A use case describes useful behavior a system provides to an actor, including relevant paths and variations. A test case specifies how to check a particular behavior, with the conditions, inputs, steps, and expected results needed to judge the outcome. Use cases help clarify what the system should do; test cases make selected checks repeatable and assessable.
What is a use case?
A use case describes actions performed by a system that produce an observable result of value to an actor or another stakeholder. The Object Management Group’s Unified Modeling Language specification (ISO/IEC 19505-2:2012, §16.3.6) defines it in those terms. It describes behavior at the system boundary rather than prescribing the internal implementation.
A use case often identifies the actor, the goal, the conditions for starting, and the main interaction path. It can also capture meaningful alternatives, exceptions, and error handling. For example, a checkout use case might describe a shopper submitting an order, then include alternatives for a declined payment or an unavailable item.
What is a test case?
A test case sets out a particular check and the expected response against which its result can be evaluated. NASA’s Software Safety Guidebook (NASA-GB-8719.13) describes a test case as documenting an input, action, or event and an expected response to determine whether an application feature works correctly.
For repeatable execution, NASA’s Software Engineering Handbook, Version B, recommends recording the requirements addressed, prerequisite conditions, test inputs, instructions, expected results, assumptions or constraints, evaluation criteria, and test configuration. In practice, a test case may include:
- Identifier and name: a unique reference and a concise description of the check.
- Objective and requirement: what behavior is being verified and which requirement it relates to.
- Preconditions and configuration: the account state, environment, setup, or other conditions needed before execution.
- Inputs and steps: the data to use and the actions to perform in order.
- Expected result and evaluation criteria: what should happen and how to decide whether the actual result passes.
Use case vs. test case
| Dimension | Use case | Test case |
|---|---|---|
| Purpose | Describe useful behavior the system offers | Check whether a behavior or requirement produces an expected result |
| Perspective | An actor’s interaction with the system boundary | A verification objective and the conditions for executing it |
| Typical content | Actors or stakeholders, system behavior, main path, and relevant alternatives | Setup, inputs, steps, expected results, evaluation criteria, and traceability |
| How teams use it | Clarify behavior and inform requirements | Execute and evaluate checks; repeat them during regression testing |
How they work together
Use cases help teams identify externally visible behavior and meaningful variations. Test cases then check selected behaviors under defined conditions. Link test cases to the relevant requirements so the team can see what each test verifies and assess coverage. NASA’s software engineering guidance emphasizes traceability and clear procedures, including expected results, so tests can be repeated and used for regression checks.
There is no universal one-use-case-to-one-test-case mapping. A use case may have several paths worth checking, and teams can choose test cases based on requirements and the coverage they need. The NASA sources support traceability and coverage, not a fixed mapping rule.
Example: placing an online order
Use case: Place an order
Actor: shopper. Goal: submit a cart and receive an order confirmation. The main path might cover reviewing the cart, entering delivery and payment details, submitting the order, and seeing confirmation. Relevant alternatives could include a payment decline or an item becoming unavailable. This describes the behavior and its variants without dictating how the store is built.
Test case: Successful payment produces confirmation
- Preconditions: the shopper has an account and a cart containing an available item; the test environment is configured to accept the payment input.
- Input: a valid payment value for that environment and the required delivery details.
- Steps: open checkout, enter the details, submit the order, and inspect the resulting page or confirmation.
- Expected result: the order is accepted and an order confirmation is shown.
- Evaluation: pass if the expected confirmation appears for the submitted order; otherwise record the actual result and mark the check accordingly.
A separate test case could check the declined-payment path, with its own input and expected result. These examples illustrate the distinction; they are not reported test results.
Use case, test case, and test scenario
“Test scenario” is sometimes used alongside “test case,” but teams and tools may use the terms differently. A scenario may refer to a broad situation or path to explore, while a test case is commonly written with the setup, inputs, steps, and expected result needed for a specific check. Agree on the terminology your team uses; the important distinction here is that a use case describes system behavior, while a test case defines a check of behavior.
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Common documentation mistakes
- Writing a test case without an expected result: without a defined outcome and evaluation criteria, it is difficult to decide whether execution passed.
- Putting implementation details in place of user-visible behavior: use cases explain what happens across the system boundary, not how the internals must be built.
- Leaving setup or inputs implicit: record prerequisites and data so another tester can reproduce the check.
- Assuming one test covers an entire use case: check relevant alternative and error paths where requirements call for them, and maintain traceability to the requirements addressed.
Screenshot evidence for browser-based test cases
When a test case checks how a page looks, a screenshot can help document the observed result; it does not by itself define whether that result meets the requirement. ScreenshotNeo is a website screenshot API and MCP server for developers. Its service can capture a page as an image or PDF, which may be useful when a browser-based test needs visual evidence. Learn more at ScreenshotNeo. Its free plan includes 1,000 screenshots per month with no card required. Sign up for ScreenshotNeo.
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