rspec

# RSpec Testing

This skill provides comprehensive guidance for writing effective RSpec tests in Ruby and Rails applications. Use for writing new specs, fixing failing tests, understanding matchers, using test doubles, and following RSpec best practices.

## Quick Reference

### Basic Structure

```ruby
RSpec.describe Order do
  subject(:order) { described_class.new(items) }
  let(:items) { [item1, item2] }
  let(:item1) { double("item", price: 10) }
  let(:item2) { double("item", price: 20) }

  describe "#total" do
    it "sums item prices" do
      expect(order.total).to eq(30)
    end
  end

  context "with discount" do
    let(:order) { described_class.new(items, discount: 5) }

    it "applies discount" do
      expect(order.total).to eq(25)
    end
  end
end
```

### Key Concepts

| Concept | Purpose |
|---------|---------|
| `describe` / `context` | Group related examples |
| `it` / `specify` | Define individual test cases |
| `let` | Lazy-evaluated, memoized helper |
| `let!` | Eager-evaluated helper (runs before each example) |
| `subject` | Primary object under test |
| `before` / `after` | Setup and teardown hooks |
| `expect` | Make assertions |

## Writing Good Specs

### Use Named Subject for Method Tests

```ruby
describe "#calculate_total" do
  subject(:total) { order.calculate_total }

  it "returns sum of items" do
    expect(total).to eq(100)
  end
end
```

### Context Blocks for Different States

```ruby
describe "#withdraw" do
  context "with sufficient funds" do
    let(:account) { build(:account, balance: 100) }

    it "reduces balance" do
      expect { account.withdraw(50) }.to change(account, :balance).by(-50)
    end
  end

  context "with insufficient funds" do
    let(:account) { build(:account, balance: 10) }

    it "raises error" do
      expect { account.withdraw(50) }.to raise_error(InsufficientFunds)
    end
  end
end
```

## Common Matchers

### Equality

```ruby
expect(x).to eq(y)          # ==
expect(x).to eql(y)         # eql