Software Testing Strategy for Custom Software
Testing isn't about achieving 100% coverage — it's about building confidence that your software works correctly in production.
Testing is the most misunderstood aspect of software development. Some teams test nothing and fix bugs in production. Others chase 100% code coverage and spend more time maintaining tests than writing features. Both approaches waste money.
A good testing strategy is pragmatic: test the things that matter, automate what's worth automating, and accept that some testing is better done manually. This guide covers how to think about testing for custom software projects.
The Testing Pyramid
The testing pyramid is still the best mental model: many fast unit tests at the base, fewer integration tests in the middle, and a small number of end-to-end tests at the top. Each layer catches different types of bugs at different costs.
Unit tests are cheap, fast, and catch logic errors. Integration tests verify that components work together correctly. End-to-end tests confirm that complete user workflows function as expected. The ratio should be roughly 70% unit, 20% integration, 10% E2E.
Unit Tests
Test individual functions and components in isolation. Fast (milliseconds), cheap to write, and catch logic bugs early.
Integration Tests
Test that components work together — API endpoints, database queries, service interactions. Slower but catch interface bugs.
E2E Tests
Test complete user workflows through the actual UI. Slowest and most brittle, but catch the bugs users would actually experience.
Visual Regression
Screenshot comparison tests that catch unintended UI changes. Essential for component libraries and design systems.
What to Test (and What Not To)
Test business logic: calculations, data transformations, permission checks, and workflow state machines. These are the things that, if broken, cause real business harm — wrong invoices, unauthorized access, lost data.
Don't test framework code: if you're writing tests that verify React renders a div, you're testing React, not your application. Don't test obvious getters/setters. Don't test third-party libraries. Focus your testing energy where it delivers the most value.
Test edge cases aggressively: empty inputs, null values, concurrent modifications, network failures, and boundary conditions. Edge cases are where most production bugs live, and they're the cases most likely to be missed in manual QA.
Test Automation vs Manual Testing
Automate tests that you run frequently: anything in your CI/CD pipeline should be automated. This includes unit tests, critical-path integration tests, and core user flow E2E tests. These run on every pull request and catch regressions before they reach production.
Keep manual testing for exploratory scenarios: usability testing, visual review of new designs, testing on physical devices, and edge cases that are expensive to automate but easy for a human to check. The goal isn't to automate everything — it's to automate the right things.
Testing in CI/CD Pipelines
Your CI/CD pipeline should run tests automatically on every code change. The pipeline should fail fast: run unit tests first (seconds), then integration tests (minutes), then E2E tests (minutes). If unit tests fail, don't waste time running slower tests.
Set quality gates: code coverage thresholds (we recommend 70-80% for business logic), zero failing tests for merge, and performance budgets for key endpoints. These gates prevent quality degradation over time.
Frequently Asked Questions
What code coverage percentage should we target?
How much time should we spend on testing?
Should we hire dedicated QA engineers?
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