API Testing Best Practices – How to Test APIs for Beginners
APIs drive huge portions of business value in modern software, forming the connections that allow modular services to communicate. However, limited testing leaves APIs vulnerable to disruptive failures. 93% of organizations have experienced an API or microservices failure in the past year.
This guide equips beginners with industry best practices for battle testing the APIs their solutions rely on.
Why Rigorously Testing APIs Matters
As services increasingly decompose into distributed microservices, the average large company juggles over 900 different APIs. Complex chains of API calls bridge these disparate systems to function cohesively from the user perspective. An individual defective link anywhere in that chain can take down the entire system.
Meticulous API testing is mandatory to prevent problems like:
| Performance issues degrading end user experience |
Security holes allowing data breaches | Downstream breaking changes after updates |
Top developers recognize comprehensive API testing as a critical element of resilience engineering. Establishing test automation early in the SDLC helps prevent snowballing technical debt.
Understanding What APIs Are
An API is an interface that defines interactions between software applications. They allow services to connect and exchange data, shielding developers from needing to know implementations.
Some examples include:
- Public APIs like Twilio for sending text messages
- Internal APIs that enable microservices to share business logic
- 3rd party APIs that feed external data into apps
API testing focuses on ensuring these interfaces handle expected and unexpected usage without flaws.
Types of API Testing
While verifying the functional outputs of API requests is vital, there are also other crucial dimensions:
1. Load Testing checks performance as traffic ramps up:
- Ensure acceptable response times as usage scales
- Identify concurrency bottlenecks under load
2. Security Testing probes for vulnerabilities:
- Attempt common attacks like SQL injections
- Verify inputs are properly sanitized
3. Reliability Testing builds confidence APIs work continuously:
- Inject faulty inputs and simulate failures
- Check resilience of fallbacks and retries
Robust testing across these areas prevents major issues down the line.
Top API Testing Tools
Specialized tools help drive efficiency in API test campaigns.
Postman
Postman is excellent for exploratory testing of APIs. Developers can quickly construct requests, inspect responses, mock servers and output collections of test cases.
Postman offers functionality like:
- GUI based interactive testing
- Scripted API test automation
- Shared workspaces and documentation
The free tier makes it easy to get started for REST API testing.
JMeter
Apache JMeter is a very popular open source load and stress testing tool useful for performance testing APIs:
Key features:
- Ability to simulate thousands of concurrent virtual users
- Build HTTP request samplers for load scenarios
- Analyze overall performance with aggregate reports
Scripting in JMeter enables you to replicate real world API usage patterns.
Rest Assured
For test automation, Rest Assured is a Java domain specific language designed to simplify API testing:
given()
.auth().oauth2(ACCESS_TOKEN)
.queryParam("type", "artist")
.when()
.get("/users/john")
.then()
.statusCode(200)
.body("id", equalTo("john123"));Benefits include:
- Clean readable test syntax
- Seamless integration into CI/CD pipelines
- Support for modern HTTP standards
The fluent API minimizes test code overhead.
Core API Testing Principles
Follow these vital guiding principles:
Shift testing left – Start validating APIs early, not after implementation. Fixing bugs later proves exponentially more expensive. | **Reliability first** – The #1 priority should be eliminating test flakiness and fragility. Reliable test automation builds confidence. |
Isolate test data – Prevent test data corruption by separating input/output from production data stores. | **Design for testability** – Building APIs specifically to simplify testing saves time over the long run. |
Delivering these principles requires forethought but pays dividends in release resilience.
Getting Started With API Test Automation
Follow these steps to implement robust automated API testing:
1. Identify Target API Use Cases
First understand real world usage flows that you need to mimic. Review documentation and inspect network traces to map out priorities.
2. Install Postman and Explore Manually
Poke around endpoints interactively to better understand expectations, options and outputs.
3. Script API Test Cases
Convert your priority user journeys into automated checks in Postman orRest Assured:
POST /users
status 201
GET /users/{userId}
status 200
body .name = "Jane" Checking status codes and key response values builds core validation.
4. Combine Test Cases into Reusable Suites
Group related test cases and data sets into suites focused onareas like authentication, payments etc.
5. Integrate With CI Pipelines
Embed test suites into continuous integration workflows enforcing API quality gates pre-merge.
Automating tests aligned to use cases provides efficiency and stability. Expanding coverage prevents regressions across updates.
API Testing Best Practices
Follow these expert tips for greater testing effectiveness:
Simulate Alternative Workflows – Exercise unexpected user behaviors exposing edge issues not triggered during happy paths. Inputting invalid or extreme data can reveal overlooked defects.
Testing Quadrants – Structure test planning based on the testing quadrants model balancing business risk vs test levels.
Dynamic Data Binding – Parameterize test steps and inputs to efficiently cover multiple scenarios with a single data driven test.
Effective Stubbing Strategies – Stub out dependencies with simulated test doubles allowing tests to run independently and avoid brittleness.
Monitor Service Virtualization – Observe API traffic profiles during tests to confirm your emulations mirror reality.
Risk Based Prioritization – Not all APIs require the same level of rigor. Focus testing queues and depths proportionally to potential business impact.
Troubleshooting API Test Failures
Tests can conversly fail for the wrong reasons. Follow these steps to properly diagnose root causes:
1. Reproduce Error Prerequisites
Confirm the precise sequence of steps leading up to failure. Identify any correlations between test runs and environments.
2. Inspect Transactions
Dig into offending requests and responses. Compare to passing runs to identify differences in headers, payload contents, formatting etc.
3. Enable Detailed Logging
Capture granular logs across all involved services showing field values. Trace request flows end-to-end through systems.
4. Validate Test Fixture Configuration
Check for any dependencies providing unexpected inputs rather than expected stubbed responses.
5. Review Code Changes
Scan code for any recent commits relevant to the failing functionality that could be contributing to regressions.
Methodically ruling out external factors and validating assumptions helps narrow root cause. Leverage logs, tools and collaboration for efficient debugging.
Conclusion
Thorough API testing delivers the confidence and resilience required from interfaces central to interconnected systems. This guide defines a plan of action allowing even beginners to start effectively testing APIs.
Leverage modern tools and automation to prevent uncaught defects. Prioritize tests reflecting real usage and risk profiles. Building API testing maturity will soon pay dividends as microservices architectures continue gaining mindshare across software development.
