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package test
// Package test provides mocks and helpers for testing code that uses slog logging.
//
// It includes MockHandler, a thread-safe slog.Handler implementation for capturing log records in tests.
import (
"context"
"log/slog"
"slices"
"sync"
"testing"
)
type logRecorder struct {
mu sync.Mutex
records []slog.Record
}
func (h *logRecorder) Append(r slog.Record) {
h.mu.Lock()
defer h.mu.Unlock()
h.records = append(h.records, r.Clone())
}
func (h *logRecorder) Records() []slog.Record {
h.mu.Lock()
defer h.mu.Unlock()
return slices.Clone(h.records)
}
// MockHandler is a slog.Handler that records log records for testing.
//
// It supports attribute and group chaining like slog's built-in handlers.
// Use NewMockLogHandler to construct one, then pass it to slog.New in your tests.
//
// All recorded logs can be retrieved with the Records method.
type MockHandler struct {
recorder *logRecorder
parent *MockHandler
group string
attrs []slog.Attr
}
var _ slog.Handler = &MockHandler{}
// NewMockLogHandler creates a new MockHandler for use in tests.
func NewMockLogHandler(tb testing.TB) *MockHandler {
tb.Helper()
return &MockHandler{
recorder: &logRecorder{},
}
}
func (h *MockHandler) Enabled(ctx context.Context, level slog.Level) bool {
return true // Capture all logs
}
func normalizeAttrs(attrs []slog.Attr) []slog.Attr {
var out []slog.Attr
for _, attr := range attrs {
if attr.Equal(slog.Attr{}) {
continue
}
v := attr.Value.Resolve()
switch v.Kind() {
case slog.KindGroup:
// Skip empty group
if len(v.Group()) == 0 {
continue
}
inner := normalizeAttrs(v.Group())
// Flatten if group key is empty
if attr.Key == "" {
out = append(out, inner...)
} else {
out = append(out, slog.Attr{
Key: attr.Key,
Value: slog.GroupValue(inner...),
})
}
default:
out = append(out, slog.Attr{
Key: attr.Key,
Value: v,
})
}
}
return out
}
func (h *MockHandler) Handle(ctx context.Context, r slog.Record) error {
newRecord := slog.NewRecord(r.Time, r.Level, r.Message, r.PC)
if h.parent == nil {
attrs := []slog.Attr{}
r.Attrs(func(attr slog.Attr) bool {
attrs = append(attrs, attr)
return true
})
attrs = normalizeAttrs(attrs)
newRecord.AddAttrs(attrs...)
h.recorder.Append(newRecord)
return nil
}
attrs := slices.Clone(h.attrs)
r.Attrs(func(attr slog.Attr) bool {
attrs = append(attrs, attr)
return true
})
attrs = normalizeAttrs(attrs)
if h.group != "" {
newRecord.AddAttrs(slog.Attr{
Key: h.group,
Value: slog.GroupValue(attrs...),
})
} else {
newRecord.AddAttrs(attrs...)
}
return h.parent.Handle(ctx, newRecord)
}
func (h *MockHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
if len(attrs) == 0 {
return h
}
return &MockHandler{
recorder: h.recorder,
parent: h,
attrs: attrs,
}
}
func (h *MockHandler) WithGroup(name string) slog.Handler {
if name == "" {
return h
}
return &MockHandler{
recorder: h.recorder,
parent: h,
group: name,
}
}
// Records returns a copy of all slog.Records captured by this handler so far.
//
// It is safe to call from multiple goroutines.
func (h *MockHandler) Records() []slog.Record {
return h.recorder.Records()
}
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