Laws of Manual Testing

jason arbon
2 min readNov 7, 2023


Bug Rate Principle

Decreasing bug rates validate effective testing.

Principle of Speed

Manual testing slows development, to speed up quality.

The Teacher Paradox

If someone is selling a philosophy of manual testing — they are wrong.

Test Count Paradox

Test counts are not correlated with value, only cost.

Law of Test Passes

The best testers continually test.

Law Of Timing

Testing should start when it makes sense, not always early.

Law Of Coverage

Estimates of code or test coverage are wrong.

Law of Smoke

Always more fire where there is smoke.

Testers be Testing Principal

Teachers and preachers. aren’t testers, beware.

Bug and Coverage Paradox

Non-testers only care about ship-blockers.

Priority principal

Test prioritization should be greatly deprioritized.

Myth of the Right Way To Test

Testing is all contextual and still an art, not a science.

Waldo Paradox

The bugs are where you haven’t looked yet.

Paradox of Quality Ownership

Testers will still be held accountable for quality, and they should be.

Law of Time

All software will break given enough time.

Insurance Principal

Testing is insurance and due diligence.

Law of Quantification

Perfectly repeatable / documented test cases are essential.

Paradox of More Testing

Diminishing returns means you always test more than you should.

Agile Myth

Agile just means ‘less waterfall’.

Law of Agile Testing

Simply test the newest stuff, and the most risky.

TDD Myth

No one does TDD.

Law of Learning

Most learning by testers should be about the world, the users and the context — not the application.

Myth of Formalization

Cucumber and User Stories are not formal methods.

Law of AI

The more a tester or vendor mentions AI, the less likely they know what it is.

Myth of Learning

If someone is ‘learning about the app’, they are just bored with testing in general.

Law of Testing Simplicity

Beware of testers redefining words, they are poor testers.

User Paradox

You are not the user.

Ratio Principle

Developer-tester ratios should be proportional to the software’s need for accuracy multiplied by its behavioral variability.

Test Marketing Paradox

The usefulness of a tool is inversely proportional to the marketing claims and price.

Tester Efficacy Paradox:

Testers add bugs, not software quality.

Reporting Principle

Other than 100%, percentages aren’t useful.

— Jason Arbon, TestNerd



jason arbon

blending humans and machines. co-founder @testdotai eater of #tunamelts