test: improve coverage across package

modifier/interface_test.go

@@ -0,0 +1,22 @@
+package modifier
+
+import (
+	"errors"
+	"testing"
+)
+
+func TestErrInvalidPacket_Error(t *testing.T) {
+	e := &ErrInvalidPacket{Err: errors.New("bad checksum")}
+	want := "invalid packet: bad checksum"
+	if got := e.Error(); got != want {
+		t.Errorf("Error() = %q, want %q", got, want)
+	}
+}
+
+func TestErrInvalidArgs_Error(t *testing.T) {
+	e := &ErrInvalidArgs{Err: errors.New("missing 'a' arg")}
+	want := "invalid args: missing 'a' arg"
+	if got := e.Error(); got != want {
+		t.Errorf("Error() = %q, want %q", got, want)
+	}
+}