demo-test-styles

Examples of Testing Strategies

In this project we'll explore different ways to use fixtures (essentially static JSON objects.)

Goals

1. Clarity in tests.
2. Tests should look more like actual implementation.
3. Explore helper functions to generate fixtures.

Test Scoping Patterns: Examples

1. Style 1: Inline Inputs & Outputs
2. Style 2: Local Helper Function
3. Style 3: Hierarchy & Scoped Tests

Project: Transaction Processor

We'll be given an array of transactions on which we'll perform operations.

Requirements

• processTotals(txs: Transactions[]) - Calculate total per BaseTransaction, by adding tax and tip to a total field.

Stretch Tasks

• sumTotal(txs: Transactions[]) - Sum of all totals in list of transactions.
• Detect invalid values (negative taxes, etc.)
• Group totals by category.

Notes

expect() Patterns

// ✅ Stable, inline values
expect(result[0].total).toBe(130.0);
expect(result[1].total).toBe(140.0);

// 🟡 No mutations*, direct field mapping to focus on the value that changed
expect(result.map(tx => tx.total)).toMatchObject([
  130.0,
  140.0,
]);

// 🔴 Repeated Calculations, may reference `result` variable
expect(result[0].total).toBe((100.0 * 1.1) + 20.0);
expect(result[1].total).toBe((100.0 * 1.1) + 30.0);