Should beginner programmers use unit testing?

Yes, beginner programmers should use unit testing on code that other people use, because a failure costs users the same whoever wrote the code. Write one test for each rule that decides a result, and run the tests in CI on every pull request.

When should a beginner start learning unit testing?

A beginner should start learning unit testing before their first project that someone else uses, the first one where a failure has a price. Exercises are cheap practice, because each lists inputs and expected outputs, which is what a test needs.

What should a beginner's first unit test check?

A beginner's first unit test should check one rule that decides a result, with an expected output worked out by hand. A test of a getter or of calls to a mock checks nothing a user sees. Break the code once to see the test fail.

Should beginners write unit tests?

Verdict

Yes

Yes, beginners should write unit tests for code that other people use, from their first task on a team: one test for each rule and boundary the change adds, with the expected value worked out by hand, run in CI on every pull request.

Why

Blast radiususers
Change frequencyregularly
Detectabilityeventually
Reversibilitywith-effort
Test costmoderate

Yes, a beginner should write unit tests for code that other people use, because the author's experience changes none of the five factors. My typical case is a developer in their first year on a team who adds a rule to a web application, such as cleaning up phone numbers on a signup form. Blast radius is users and Change frequency is regularly, about once a month. Detectability is eventually, because a wrong rule returns a plausible value that a reviewer can miss, and Reversibility is with-effort, since saved records need a repair script. Test cost is moderate, about an hour, which a beginner spends reading the team's suite and working out the expected values by hand, so rule R11 gives Test.

When the decision changes
When	Decision	Why
The code is a course exercise that only you run and then delete	Do not test to protect the exercise; check its output against the worked examples	Blast radius falls to none: only you run the exercise and bear a failure
Your first public project has a few dozen users, redeploys from the repository, and stores nothing users cannot rebuild	Test minimally: one test of the main path, plus a regression test for each bug	Reversibility falls to trivial: a redeploy of the previous commit undoes the failure
The task changes a label or a colour that you see on screen right after the change	Do not test; look at the page before the merge	Detectability moves to immediately and Reversibility to trivial: you see the mistake, and a revert removes it
The rule computes a price, a discount or an invoice total	Test mandatory: every amount, the rounding and the boundary values, with a senior developer reviewing the tests	Blast radius rises to money and Reversibility to costly: a wrong charge ends in refunds
The code decides which user may read which record	Test mandatory: one allowed and one denied case for each role	Blast radius rises to safety-or-legal and Detectability to never: a leaked record raises no error

What breaks if you don't test

An untested rule breaks on the input its author did not try, such as a number with a country code. The reviewer approves the change, customers meet the failure weeks later, and every record saved since the merge needs a repair script.

What you lose if you over-test

Beginners often test everything they can reach: getters, private helpers and each call a controller makes to a mock. Those tests fail on refactors that keep behaviour the same, so the beginner learns to edit tests until they pass, and coverage rises while no test checks a result a customer sees.

How to test

Pick the rules in your change that decide a result, such as a validation, and leave glue code to the team's endpoint tests.
Work the expected value out by hand from the ticket before you run the code.
Copy an existing test from the team's suite and run it with pytest, JUnit 5 or the team's runner.
Break the code once and check that the test fails.

Procedure and references

When the answer changes

The code moves money or decides who may see a record.
Only you run the code, as with course exercises, which stay a cheap place to practise tests.
Your team requires a test with every change: follow the team rule.

Real incident + Code example

The phone numbers that lost their plus

On a class booking app for a chain of gyms, the first task of a junior developer on my team was normalize_phone, which cleaned up numbers from the signup form. It removed every character that was not a digit, including the plus of international numbers. I approved the pull request, because every number she had tried was local. For 19 days, 212 members saved numbers that the text message service rejected, and the rejections went to a log nobody read until a member asked why her class reminders had stopped. A script rebuilt most numbers from the signup log, and staff asked 40 members in person. The fix went in with these tests:

from members.phone import normalize_phone

def test_keeps_the_plus_of_an_international_number():
    assert normalize_phone("+33 6 12 34 56 78") == "+33612345678"

def test_turns_a_leading_00_into_a_plus():
    assert normalize_phone("0033 6 12 34 56 78") == "+33612345678"

def test_adds_the_country_code_to_a_local_number():
    assert normalize_phone("07700 900123", country="GB") == "+447700900123"

Should developers write their own tests?Code under test: Yes
Is unit testing worth it?Yes
Should I write tests before code?Code under test: Yes
Should I use TDD?Code under test: Yes
Should I write tests for side projects?Yes

FAQ

Should beginner programmers use unit testing?: Yes, beginner programmers should use unit testing on code that other people use, because a failure costs users the same whoever wrote the code. Write one test for each rule that decides a result, and run the tests in CI on every pull request.
When should a beginner start learning unit testing?: A beginner should start learning unit testing before their first project that someone else uses, the first one where a failure has a price. Exercises are cheap practice, because each lists inputs and expected outputs, which is what a test needs.
What should a beginner's first unit test check?: A beginner's first unit test should check one rule that decides a result, with an expected output worked out by hand. A test of a getter or of calls to a mock checks nothing a user sees. Break the code once to see the test fail.