test: add mock-based site extractor test infrastructure

Create exported extractortest package with MockBrowser, MockDocument,
and MockNode that support selector-based responses for testing site
extractors without a real browser.

Add extraction tests for DuckDuckGo (result parsing, empty results, no
links, full search flow) and Powerball (drawing parsing, next drawing
parsing with billion/million, error cases, full GetCurrent flow).

Closes #21
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

extractortest/mock.go

@@ -0,0 +1,103 @@
+// Package extractortest provides mock implementations of the extractor
+// interfaces for use in unit tests. The mocks support selector-based
+// responses so site extractors can exercise their parsing logic without
+// a real browser.
+package extractortest
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"gitea.stevedudenhoeffer.com/steve/go-extractor"
+)
+
+// MockNode implements extractor.Node with configurable selector responses.
+type MockNode struct {
+	TextValue    string
+	TextErr      error
+	ContentValue string
+	Attrs        map[string]string
+	// Children maps CSS selectors to the nodes that should be returned.
+	Children map[string]extractor.Nodes
+}
+
+var _ extractor.Node = &MockNode{}
+
+func (m *MockNode) Content() (string, error) { return m.ContentValue, nil }
+func (m *MockNode) Text() (string, error)    { return m.TextValue, m.TextErr }
+
+func (m *MockNode) Attr(name string) (string, error) {
+	if m.Attrs == nil {
+		return "", nil
+	}
+	v, ok := m.Attrs[name]
+	if !ok {
+		return "", nil
+	}
+	return v, nil
+}
+
+func (m *MockNode) Screenshot() ([]byte, error)        { return nil, nil }
+func (m *MockNode) Type(_ string) error                 { return nil }
+func (m *MockNode) Click() error                        { return nil }
+func (m *MockNode) SetHidden(_ bool) error              { return nil }
+func (m *MockNode) SetAttribute(_, _ string) error      { return nil }
+
+func (m *MockNode) Select(selector string) extractor.Nodes {
+	if m.Children == nil {
+		return nil
+	}
+	return m.Children[selector]
+}
+
+func (m *MockNode) SelectFirst(selector string) extractor.Node {
+	return m.Select(selector).First()
+}
+
+func (m *MockNode) ForEach(selector string, fn func(extractor.Node) error) error {
+	nodes := m.Select(selector)
+	for _, n := range nodes {
+		if err := fn(n); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// MockDocument implements extractor.Document with configurable selector responses.
+type MockDocument struct {
+	MockNode
+	URLValue string
+}
+
+var _ extractor.Document = &MockDocument{}
+
+func (m *MockDocument) URL() string                             { return m.URLValue }
+func (m *MockDocument) Refresh() error                          { return nil }
+func (m *MockDocument) Close() error                            { return nil }
+func (m *MockDocument) WaitForNetworkIdle(_ *time.Duration) error { return nil }
+
+// Content on MockDocument returns its own ContentValue (overrides embedded MockNode).
+func (m *MockDocument) Content() (string, error) { return m.ContentValue, nil }
+
+// MockBrowser implements extractor.Browser. Configure Documents to map URLs
+// to MockDocuments that will be returned from Open.
+type MockBrowser struct {
+	Documents map[string]*MockDocument
+}
+
+var _ extractor.Browser = &MockBrowser{}
+
+func (m *MockBrowser) Close() error { return nil }
+
+func (m *MockBrowser) Open(_ context.Context, url string, _ extractor.OpenPageOptions) (extractor.Document, error) {
+	if m.Documents == nil {
+		return nil, fmt.Errorf("no documents configured")
+	}
+	doc, ok := m.Documents[url]
+	if !ok {
+		return nil, fmt.Errorf("no mock document for URL %q", url)
+	}
+	return doc, nil
+}