Add comprehensive test suite for v2 module with mock provider

Cover all core library logic (Client, Model, Chat, middleware, streaming,
message conversion, request building) using a configurable mock provider
that avoids real API calls. ~50 tests across 7 files.

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

v2/mock_provider_test.go

@@ -0,0 +1,87 @@
+package llm
+
+import (
+	"context"
+	"sync"
+
+	"gitea.stevedudenhoeffer.com/steve/go-llm/v2/provider"
+)
+
+// mockProvider is a configurable mock implementation of provider.Provider for testing.
+type mockProvider struct {
+	CompleteFunc func(ctx context.Context, req provider.Request) (provider.Response, error)
+	StreamFunc   func(ctx context.Context, req provider.Request, events chan<- provider.StreamEvent) error
+
+	// mu guards Requests
+	mu       sync.Mutex
+	Requests []provider.Request
+}
+
+func (m *mockProvider) Complete(ctx context.Context, req provider.Request) (provider.Response, error) {
+	m.mu.Lock()
+	m.Requests = append(m.Requests, req)
+	m.mu.Unlock()
+	return m.CompleteFunc(ctx, req)
+}
+
+func (m *mockProvider) Stream(ctx context.Context, req provider.Request, events chan<- provider.StreamEvent) error {
+	m.mu.Lock()
+	m.Requests = append(m.Requests, req)
+	m.mu.Unlock()
+	if m.StreamFunc != nil {
+		return m.StreamFunc(ctx, req, events)
+	}
+	close(events)
+	return nil
+}
+
+// lastRequest returns the most recent request recorded by the mock.
+func (m *mockProvider) lastRequest() provider.Request {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if len(m.Requests) == 0 {
+		return provider.Request{}
+	}
+	return m.Requests[len(m.Requests)-1]
+}
+
+// newMockProvider creates a mock that always returns the given response.
+func newMockProvider(resp provider.Response) *mockProvider {
+	return &mockProvider{
+		CompleteFunc: func(ctx context.Context, req provider.Request) (provider.Response, error) {
+			return resp, nil
+		},
+	}
+}
+
+// newMockProviderFunc creates a mock with a custom Complete function.
+func newMockProviderFunc(fn func(ctx context.Context, req provider.Request) (provider.Response, error)) *mockProvider {
+	return &mockProvider{CompleteFunc: fn}
+}
+
+// newMockStreamProvider creates a mock that streams the given events.
+func newMockStreamProvider(events []provider.StreamEvent) *mockProvider {
+	return &mockProvider{
+		CompleteFunc: func(ctx context.Context, req provider.Request) (provider.Response, error) {
+			return provider.Response{}, nil
+		},
+		StreamFunc: func(ctx context.Context, req provider.Request, ch chan<- provider.StreamEvent) error {
+			for _, ev := range events {
+				select {
+				case ch <- ev:
+				case <-ctx.Done():
+					return ctx.Err()
+				}
+			}
+			return nil
+		},
+	}
+}
+
+// newMockModel creates a *Model backed by the given mock provider.
+func newMockModel(p *mockProvider) *Model {
+	return &Model{
+		provider: p,
+		model:    "mock-model",
+	}
+}