diff --git a/pkg/schema/err_test.go b/pkg/schema/err_test.go
new file mode 100644
index 0000000..17ef5d9
--- /dev/null
+++ b/pkg/schema/err_test.go
@@ -0,0 +1,31 @@
+package schema
+
+import "testing"
+
+func TestCircularError(t *testing.T) {
+	tests := []struct {
+		name    string
+		message string
+		want    string
+	}{
+		{
+			name:    "basic error message",
+			message: "circular dependency detected",
+			want:    "circular dependency detected",
+		},
+		{
+			name:    "empty message",
+			message: "",
+			want:    "",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := &CircularError{msg: tt.message}
+			if got := err.Error(); got != tt.want {
+				t.Errorf("CircularError.Error() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}