Glossary: transactions, inferred types and unit tests — DedSec Project

Transaction

Actual meaning

A unit of database work committed together or rolled back together. Atomicity does not mean every race is solved; isolation level and concurrent writers remain relevant.

Concrete starting point

BEGIN;
INSERT INTO tasks(title) VALUES ('first');
-- perform other work
ROLLBACK;

Apply the rule

In disposable SQLite, prove a row inserted inside a rolled-back transaction does not persist, then compare with a committed insert.

Diagnose a counterexample

For Transaction, write down the expected outcome, deliberately break an assumption from this specific example, and determine what must be checked at the boundary before this behavior could be reused safely.

Type inference

Actual meaning

Compiler derives a type from context without explicit annotation. This is still static typing where the language enforces it; inference does not mean treating all values as any.

Concrete starting point

const scores: number[] = [2,4];
const doubled = scores.map(n => n*2);
// n inferred number

Apply the rule

Make the array string[], attempt numeric multiplication and inspect the TypeScript diagnostic. Compare inference with an explicit wrong annotation.

Diagnose a counterexample

For Type inference, write down the expected outcome, deliberately break an assumption from this specific example, and determine what must be checked at the boundary before this behavior could be reused safely.

Unit test

Actual meaning

Small repeatable check of a focused behavior with controlled inputs. Unit tests differ from integration tests involving real databases, browsers or network services.

Concrete starting point

def clamp(x, lo, hi): return min(max(x,lo),hi)
assert clamp(5,0,10)==5
assert clamp(-1,0,10)==0

Apply the rule

Add exact boundary checks 0 and 10, then decide whether lo>hi should raise rather than return an accidental value.

Diagnose a counterexample

For Unit test, write down the expected outcome, deliberately break an assumption from this specific example, and determine what must be checked at the boundary before this behavior could be reused safely.

WebSocket

Actual meaning

Protocol for ongoing bidirectional communication over a connection, commonly initiated by an HTTP Upgrade handshake. Unlike one-shot HTTP requests, clients need connection lifecycle and reconnect policy.

Concrete starting point

const ws = new WebSocket('wss://example.test/echo');
ws.addEventListener('message', e => console.log(e.data));
// Requires an authorized matching server.

Apply the rule

Build a local test server and verify open/message/close states. Explain why reconnecting should not repeat side-effecting messages blindly.

Yield

Actual meaning

A construct suspending a generator and producing a value while preserving its execution state. It differs from return, which finishes the function invocation.

Concrete starting point

def counter():
    yield 1
    yield 2
assert list(counter())==[1,2]

Apply the rule

Call next repeatedly, then confirm StopIteration after the last value. Compare generator with a function returning [1,2] eagerly.

Diagnose a counterexample

For Yield, write down the expected outcome, deliberately break an assumption from this specific example, and determine what must be checked at the boundary before this behavior could be reused safely.