Guidelines for Creating Effective Test Plans: Balancing Cost, Risk, and Benefits

Creating a test strategy is often a complex task. An ideal strategy balances implementation cost, maintenance cost, monetary cost, benefits, and risk using basic cost‑benefit and risk‑analysis principles.

Implementation cost : The time and complexity of implementing testable features and automated tests vary by scenario, affecting short‑term development cost.

Maintenance cost : Some tests or test plans are easy to maintain, others are not, influencing long‑term development cost; manual testing also raises long‑term cost.

Monetary cost : Certain testing methods may require paid resources.

Benefits : Testing prevents problems and improves productivity; the earlier defects are found in the development lifecycle, the greater the benefit.

Risk : Failure probability can be rare or common, with consequences ranging from minor disruption to catastrophic outcomes.

Effectively balancing these factors in a test plan depends largely on project criticality, implementation details, available resources, and team input.

Many projects achieve excellent coverage with efficient, low‑cost unit tests, though they may need to trade off against larger‑scale tests and complex corner cases.

Task‑critical projects must minimize risk as much as possible, accepting higher costs and investing heavily in rigorous testing at all levels.

This guide helps readers find the right balance for their projects.

Note: This article does not provide a test‑plan template, as templates quickly become either too generic or too specific; instead it focuses on how to choose the best content when writing a test plan.

1. Test Plan vs. Test Strategy

Before proceeding, clarify the two common approaches to defining a test plan:

Single test plan : Some projects have one "test plan" describing all implemented and planned tests.

One test strategy and multiple test plans : Some projects have a "test strategy" document covering overall testing methods and goals, plus many smaller "test plans" for specific features or updates.

Either approach can be embedded and integrated with project design documents.

Both are effective; choose the one that makes sense for your project.

Generally, stable projects can use a single test plan, while rapidly changing projects benefit from a stable test strategy combined with frequently revised test plans.

In this guide, both document types are simply referred to as "test plans"; if you have multiple documents, apply the following advice to the aggregate.

2. Selecting Test Content

A good way to create concrete content for your test plan is to start by listing all questions that need answering. Review the list below, select the applicable items, and answer the questions to determine what should be included in the test plan, balancing the earlier‑mentioned factors.

Pre‑conditions

Do you need a test plan? If there is no design document or clear product vision, writing a test plan may be premature.

Is testability considered in the project design? All scenarios should be designed to be testable, preferably automatically, before implementation begins.

Can you keep the plan up‑to‑date? Avoid adding excessive detail that makes maintenance difficult.

Does the quality work overlap with other teams? If so, describe how duplication is eliminated.

Risk

What major project risks exist and how will you mitigate them? Consider user data security, privacy, system security, hardware loss, legal/compliance issues, data loss, revenue loss, unrecoverable scenarios, SLA, performance, misleading users, impact on other projects, public image, productivity loss, etc.

What technical vulnerabilities does the project have? Consider known broken or fragile components, problematic dependencies, potential user‑caused damage, and recent trends.

Coverage

What does the test interface look like? Describe whether the system is a simple library with one method or a multi‑platform client‑server system, highlighting potential failure points.

Which platforms are supported? List operating systems, hardware, devices, etc., and describe how each platform will be tested and reported.

What features are covered? Summarize features and explain how tests are designed for each category.

What is not tested? Be honest about exclusions and provide reasons (low‑priority, low‑risk, already covered elsewhere, not ready for testing, etc.).

What is included in unit, integration, and system tests? Emphasize testing as much as possible at the unit level, leaving fewer cases for larger‑scale tests.

Which tests are manual vs. automated? Automate when feasible and cost‑effective; justify any manual testing.

How do you cover each test category? Consider accessibility, functionality, circuit‑breaker, i18n/l10n, performance/load/soak, privacy, security, smoke, stability, usability.

Will you use static and/or dynamic analysis tools? Both can uncover issues hard to catch in code review and testing.

How will system components and dependencies be stubbed, mocked, faked, staged, or used directly? Provide rationale for each choice and its impact on coverage.

What build versions will your tests run against? Clarify whether tests target HEAD builds, UAT builds, candidate releases, and how version‑specific testing is handled.

What testing will be performed outside your team? Examples: dog‑fooding, crowdsourced testing, public alpha/beta testing, external trusted testers.

How is data migration tested? Include special tests to compare pre‑ and post‑migration results.

Do you need to consider backward compatibility? Account for previously shipped clients or systems that depend on your APIs or behavior.

Do you need to test upgrade scenarios for servers/clients/devices or their dependencies/platforms/APIs?

Do you have line‑coverage goals?

3. Tools and Infrastructure

Do you need a new testing framework? If so, describe it in the test plan and provide design links.

Do you need a new test lab? Describe it or link to its design.

If your project provides a service to other projects, do you offer testing tools? Consider providing mocks, fakes, and reliable staged servers for integration testing.

How do you manage end‑to‑end test infrastructure, systems, and dependencies? Explain deployment, persistence handling, and cross‑data‑center migration.

Do you need tools to help debug system or test failures? Use existing tools or develop new ones as needed.

4. Process

Are there test schedule requirements? State time commitments, which tests run when, and relative importance of tests.

How are builds and tests continuously run? Small tests often run via CI; large tests may need selective execution.

How are build and test results reported and monitored? Team rotation for CI monitoring? Specialist monitoring for large tests? Dashboard for test results and health metrics? Email alerts recipients and delivery method? Is monitoring purely verbal or does it follow a defined process?

How are test cases used at release time? Are they run only for a candidate release or does the release depend on continuous test results? If components are released independently, are specific tests run for each type of release? Do “blocking release” bugs truly block a release, and is there a shared definition of “blocking release”? During canary/rolling releases, how is monitoring and test progress handled?

How do external users report bugs? Provide dedicated feedback links or tools.

How does bug classification work? Use tags or categories to ensure bugs are placed in the correct bucket; ensure the team responsible for triage knows the system.

Do you have a policy that closing a bug must be accompanied by a new automated test?

How are test cases used for uncommitted changes? Provide a “how‑to” guide for running all automated tests on experimental builds.

How do team members create and debug a test case? Offer a “how‑to” guide.

5. Utility

Who are the readers of the test plan? Some plans have few readers, others many; ensure all stakeholders (project managers, tech leads, feature owners) review it and provide a contact for further information.

How do readers review the actual test cases? Store manual test cases in a test‑case management tool or document, and provide links to automated test directories.

Do you need traceability between requirements, features, and test cases?

Do you have generic product health or quality goals and how do you measure success? Examples: release cadence, bugs found in production, bugs found during testing, open bugs over time, code coverage, manual test cost, difficulty of creating new automated tests.

6. Afterword

Most Google projects do not use manual testing and rely entirely on automated testing, especially for backend/core/infrastructure projects.

If you ask Google whether their testing is in one of two states:

Have we automated the tests we consider necessary?

Have we truly automated every possible scenario and input/state combination?

Usually the answer is the former, because cost considerations typically prevent testing every possible permutation.

Published: July 2006, 2016

Original author: Anthony Vallone

Original link: https://testing.googleblog.com/2016/06/the-inquiry-method-for-test-planning.html