feat: add test framework & refactor RPC server (#2579)

Co-authored-by: Rene Jochum <rene@jochum.dev>

selector/default.go

@@ -1,8 +1,11 @@
 package selector
 
 import (
+	"sync"
 	"time"
 
+	"github.com/pkg/errors"
+
 	"go-micro.dev/v4/registry"
 	"go-micro.dev/v4/registry/cache"
 )
@@ -10,19 +13,25 @@ import (
 type registrySelector struct {
 	so Options
 	rc cache.Cache
+	mu sync.RWMutex
 }
 
 func (c *registrySelector) newCache() cache.Cache {
 	opts := make([]cache.Option, 0, 1)
+
 	if c.so.Context != nil {
 		if t, ok := c.so.Context.Value("selector_ttl").(time.Duration); ok {
 			opts = append(opts, cache.WithTTL(t))
 		}
 	}
+
 	return cache.New(c.so.Registry, opts...)
 }
 
 func (c *registrySelector) Init(opts ...Option) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
 	for _, o := range opts {
 		o(&c.so)
 	}
@@ -38,6 +47,9 @@ func (c *registrySelector) Options() Options {
 }
 
 func (c *registrySelector) Select(service string, opts ...SelectOption) (Next, error) {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+
 	sopts := SelectOptions{
 		Strategy: c.so.Strategy,
 	}
@@ -51,9 +63,10 @@ func (c *registrySelector) Select(service string, opts ...SelectOption) (Next, e
 	// if that fails go directly to the registry
 	services, err := c.rc.GetService(service)
 	if err != nil {
-		if err == registry.ErrNotFound {
+		if errors.Is(err, registry.ErrNotFound) {
 			return nil, ErrNotFound
 		}
+
 		return nil, err
 	}
 
@@ -87,6 +100,7 @@ func (c *registrySelector) String() string {
 	return "registry"
 }
 
+// NewSelector creates a new default selector.
 func NewSelector(opts ...Option) Selector {
 	sopts := Options{
 		Strategy: Random,