refactor(netxlite/mocks): group tests, fix naming inconsistencies (#485)

Part of https://github.com/ooni/probe/issues/1591

internal/netxlite/mocks/reader_test.go

@@ -5,19 +5,21 @@ import (
 	"testing"
 )
 
-func TestReaderRead(t *testing.T) {
-	expected := errors.New("mocked error")
-	r := &Reader{
-		MockRead: func(b []byte) (int, error) {
-			return 0, expected
-		},
-	}
-	b := make([]byte, 128)
-	count, err := r.Read(b)
-	if !errors.Is(err, expected) {
-		t.Fatal("unexpected error", err)
-	}
-	if count != 0 {
-		t.Fatal("unexpected count", count)
-	}
+func TestReader(t *testing.T) {
+	t.Run("Read", func(t *testing.T) {
+		expected := errors.New("mocked error")
+		r := &Reader{
+			MockRead: func(b []byte) (int, error) {
+				return 0, expected
+			},
+		}
+		b := make([]byte, 128)
+		count, err := r.Read(b)
+		if !errors.Is(err, expected) {
+			t.Fatal("unexpected error", err)
+		}
+		if count != 0 {
+			t.Fatal("unexpected count", count)
+		}
+	})
 }