refactor: move ErrorWrapperResolver to errorsx pkg (#419)

Part of https://github.com/ooni/probe/issues/1505

internal/errorsx/resolver_test.go

@@ -0,0 +1,80 @@
+package errorsx
+
+import (
+	"context"
+	"errors"
+	"net"
+	"testing"
+
+	"github.com/ooni/probe-cli/v3/internal/netxmocks"
+)
+
+func TestErrorWrapperResolverSuccess(t *testing.T) {
+	orig := []string{"8.8.8.8"}
+	r := &ErrorWrapperResolver{
+		Resolver: &netxmocks.Resolver{
+			MockLookupHost: func(ctx context.Context, domain string) ([]string, error) {
+				return orig, nil
+			},
+		},
+	}
+	addrs, err := r.LookupHost(context.Background(), "dns.google.com")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(addrs) != len(orig) || addrs[0] != orig[0] {
+		t.Fatal("not the result we expected")
+	}
+}
+
+func TestErrorWrapperResolverFailure(t *testing.T) {
+	r := &ErrorWrapperResolver{
+		Resolver: &netxmocks.Resolver{
+			MockLookupHost: func(ctx context.Context, domain string) ([]string, error) {
+				return nil, errors.New("no such host")
+			},
+		},
+	}
+	ctx := context.Background()
+	addrs, err := r.LookupHost(ctx, "dns.google.com")
+	if addrs != nil {
+		t.Fatal("expected nil addr here")
+	}
+	var errWrapper *ErrWrapper
+	if !errors.As(err, &errWrapper) {
+		t.Fatal("cannot properly cast the returned error")
+	}
+	if errWrapper.Failure != FailureDNSNXDOMAINError {
+		t.Fatal("unexpected failure")
+	}
+	if errWrapper.Operation != ResolveOperation {
+		t.Fatal("unexpected Operation")
+	}
+}
+
+func TestErrorWrapperResolverChildNetworkAddress(t *testing.T) {
+	r := &ErrorWrapperResolver{Resolver: &netxmocks.Resolver{
+		MockNetwork: func() string {
+			return "udp"
+		},
+		MockAddress: func() string {
+			return "8.8.8.8:53"
+		},
+	}}
+	if r.Network() != "udp" {
+		t.Fatal("invalid Network")
+	}
+	if r.Address() != "8.8.8.8:53" {
+		t.Fatal("invalid Address")
+	}
+}
+
+func TestErrorWrapperResolverNoChildNetworkAddress(t *testing.T) {
+	r := &ErrorWrapperResolver{Resolver: &net.Resolver{}}
+	if r.Network() != "errorWrapper" {
+		t.Fatal("invalid Network")
+	}
+	if r.Address() != "" {
+		t.Fatal("invalid Address")
+	}
+}