BA-14 · LESSON 03

Functional and unit testing

KEY DEFINITIONS

Terms used in this lesson

RPC: Remote procedure call: the command interface applications use to ask a Bitcoin node to perform operations or return state.
Oracle: A system that reports outside information, such as a market price, for use by a protocol.
P2P: Peer-to-peer: nodes communicate directly with other nodes rather than through one central server.
UTXO: Unspent transaction output: one discrete chunk of bitcoin that can be used as a transaction input.
Regtest: A private Bitcoin test network where the operator can create blocks instantly for repeatable experiments.

Good tests isolate consensus logic, RPC behavior, wallet state, serialization, and end-to-end node interactions.

55 min Difficulty 3/5 Not started

VISUAL MODEL

See the whole mechanism before going step by step

Use the diagrams to orient yourself. Then the guided explanation below teaches every part in depth.

4 explanatory views

CONCEPT-SPECIFIC MAP · state machineOne valid action transforms a known stateSelect any state to inspect its exact role.

RELATIONSHIP MAPOrdered mechanism flow

01
BEFOREKnown state
Identify the facts and objects that exist before the action.
02
ACTIONFunctional and unit testing
The Functional and unit testing lesson isolates the event that proposes a change.
03
RULEDeterministic check
The enforcing rule accepts or rejects the proposed transition.
04
AFTERSuccessor state
Accepted work creates a new state without silently changing the prior facts.
05
FAILUREState unchanged
A failed condition must not produce a partially accepted successor.

Rule shown: A valid transition names the prior state, action, enforcing rule, and successor state.

STAGE 1 OF 5BEFORE: Known state

Identify the facts and objects that exist before the action.

Governing relationship: A valid transition names the prior state, action, enforcing rule, and successor state. Complete path: 1. BEFORE, Known state. Identify the facts and objects that exist before the action. 2. ACTION, Functional and unit testing. The Functional and unit testing lesson isolates the event that proposes a change. 3. RULE, Deterministic check. The enforcing rule accepts or rejects the proposed transition. 4. AFTER, Successor state. Accepted work creates a new state without silently changing the prior facts. 5. FAILURE, State unchanged. A failed condition must not produce a partially accepted successor.

1. State transitionWhat exists, what changes, and what results

BEFORE

Function receives input values [70,000, 45,000] and output values [80,000, 33,800].

MECHANISM

Define an exact rule such as input value equals outputs plus fee, invalid signature leaves state unchanged, or reorg replay restores the same UTXO root.

AFTER

Different test layers provide independent evidence when their expectations are specified outside the implementation path.

Text equivalent: Starting from Function receives input values [70,000, 45,000] and output values [80,000, 33,800]. The mechanism begins when Define an exact rule such as input value equals outputs plus fee, invalid signature leaves state unchanged, or reorg replay restores the same UTXO root. The resulting lesson is Different test layers provide independent evidence when their expectations are specified outside the implementation path.

2. Mechanism pathSelect a stage to inspect its job

STAGE 1 OF 5

State one invariant

Define an exact rule such as input value equals outputs plus fee, invalid signature leaves state unchanged, or reorg replay restores the same UTXO root.

Complete path: 1. State one invariant: Define an exact rule such as input value equals outputs plus fee, invalid signature leaves state unchanged, or reorg replay restores the same UTXO root. 2. Choose the smallest useful boundary: Use unit tests for pure serialization and validation helpers, functional tests for node behavior, and end-to-end tests only when the full integration is the subject. 3. Arrange deterministic inputs: Pin network, time, randomness, keys, blocks, and dependency versions so failures reproduce. 4. Assert outputs and side effects: Check returned values, errors, database state, emitted events, files, and cleanup, including that rejected operations change nothing. 5. Cover adversarial transitions: Exercise boundaries, malformed fields, duplicates, reorgs, interruption, restart, and resource limits in addition to happy paths.

3. Rule and failure boundaryWhat accepts the result and where it can stop

ACCEPTED PATH

The chosen layer must execute a case-specific fixture against an implementation path and a separate oracle, then compare exact artifacts, state, side effects, and rejection nonmutation.

CHANGED CONDITION

Filler prose, a circular oracle, an unexecuted fixture, mismatched artifacts, wrong layer, unexpected mutation, or missing side-effect assertion cannot pass.

Important distinction: End-to-end tests are always better because they exercise more code. They catch integration failures but are slower and harder to diagnose. Focused unit and functional tests provide precision, while end-to-end tests cover selected complete workflows.

Text equivalent: The accepted path is enforced by The chosen layer must execute a case-specific fixture against an implementation path and a separate oracle, then compare exact artifacts, state, side effects, and rejection nonmutation. If the required condition changes, Filler prose, a circular oracle, an unexecuted fixture, mismatched artifacts, wrong layer, unexpected mutation, or missing side-effect assertion cannot pass.

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Learn the idea

A unit test checks a small function with controlled dependencies. A functional test runs components through public interfaces such as RPC and P2P. An integration test checks components together, while an end-to-end test follows the complete user workflow. A test oracle is the independently specified expected result, not the same code path under test.

GUIDED EXPLANATION1/5 ideas inspected

State one invariant

Define an exact rule such as input value equals outputs plus fee, invalid signature leaves state unchanged, or reorg replay restores the same UTXO root.

The worked example follows the explanation

Inspect every idea above to open it.

Important distinction“End-to-end tests are always better because they exercise more code.”

They catch integration failures but are slower and harder to diagnose. Focused unit and functional tests provide precision, while end-to-end tests cover selected complete workflows.

FINISH LEARNING FIRST

The questions unlock after every required learning activity

Inspect every guided idea, open the worked example, rebuild its mechanism, and complete the deterministic lesson tool. Your progress is saved automatically.