diff --git a/error/Error_test.go b/error/Error_test.go
new file mode 100644
index 0000000..f0f519b
--- /dev/null
+++ b/error/Error_test.go
@@ -0,0 +1,88 @@
+package virerr
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+)
+
+func TestVirError_Error(t *testing.T) {
+	if NoSuchDomain.Error() != "Domain Not Found" {
+		t.Errorf("unexpected: %s", NoSuchDomain.Error())
+	}
+}
+
+func TestErrorDescriptor_Error(t *testing.T) {
+	err := ErrorGen(NoSuchDomain, fmt.Errorf("detail"))
+	want := "(Error Type= 'Domain Not Found',\n Message='detail')"
+	if err.Error() != want {
+		t.Errorf("expected %q, got %q", want, err.Error())
+	}
+}
+
+func TestErrorDescriptor_Is(t *testing.T) {
+	err := ErrorGen(LackCapacityRAM, fmt.Errorf("oom"))
+
+	if !errors.Is(err, LackCapacityRAM) {
+		t.Error("expected errors.Is to match LackCapacityRAM")
+	}
+	if errors.Is(err, LackCapacityCPU) {
+		t.Error("expected errors.Is NOT to match LackCapacityCPU")
+	}
+}
+
+func TestErrorDescriptor_As(t *testing.T) {
+	err := ErrorGen(InvalidUUID, fmt.Errorf("bad uuid"))
+
+	var vt VirError
+	if !errors.As(err, &vt) {
+		t.Fatal("errors.As should succeed")
+	}
+	if vt != InvalidUUID {
+		t.Errorf("expected InvalidUUID, got %s", vt)
+	}
+}
+
+func TestErrorGen(t *testing.T) {
+	detail := fmt.Errorf("inner")
+	err := ErrorGen(SnapshotError, detail)
+
+	desc, ok := err.(ErrorDescriptor)
+	if !ok {
+		t.Fatal("ErrorGen should return ErrorDescriptor")
+	}
+	if desc.ErrorType != SnapshotError {
+		t.Errorf("wrong ErrorType: %s", desc.ErrorType)
+	}
+	if desc.Detail != detail {
+		t.Errorf("wrong Detail: %v", desc.Detail)
+	}
+}
+
+func TestErrorJoin_withErrorDescriptor(t *testing.T) {
+	base := ErrorGen(DomainSearchError, fmt.Errorf("original"))
+	joined := ErrorJoin(base, fmt.Errorf("appended"))
+
+	desc, ok := joined.(ErrorDescriptor)
+	if !ok {
+		t.Fatal("ErrorJoin should return ErrorDescriptor")
+	}
+	if desc.ErrorType != DomainSearchError {
+		t.Errorf("wrong ErrorType: %s", desc.ErrorType)
+	}
+	if !errors.Is(joined, DomainSearchError) {
+		t.Error("errors.Is should still match after join")
+	}
+}
+
+func TestErrorJoin_withPlainError(t *testing.T) {
+	base := fmt.Errorf("plain error")
+	joined := ErrorJoin(base, fmt.Errorf("extra"))
+
+	if joined == nil {
+		t.Fatal("ErrorJoin should not return nil")
+	}
+	if !errors.As(joined, new(VirError)) {
+		t.Error("ErrorJoin on plain error should wrap into ErrorDescriptor")
+	}
+}