Add dbx library: PostgreSQL cluster with master/replica routing, retry, health checking

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

errors_test.go

@@ -0,0 +1,92 @@
+package dbx
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/jackc/pgx/v5/pgconn"
+)
+
+func TestIsRetryable(t *testing.T) {
+	tests := []struct {
+		name string
+		err  error
+		want bool
+	}{
+		{"nil", nil, false},
+		{"generic", errors.New("oops"), false},
+		{"serialization_failure", &pgconn.PgError{Code: "40001"}, true},
+		{"deadlock", &pgconn.PgError{Code: "40P01"}, true},
+		{"too_many_connections", &pgconn.PgError{Code: "53300"}, true},
+		{"connection_exception", &pgconn.PgError{Code: "08006"}, true},
+		{"constraint_violation", &pgconn.PgError{Code: "23505"}, false},
+		{"syntax_error", &pgconn.PgError{Code: "42601"}, false},
+		{"connection_refused", errors.New("connection refused"), true},
+		{"EOF", errors.New("unexpected EOF"), true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := IsRetryable(tt.err); got != tt.want {
+				t.Errorf("IsRetryable(%v) = %v, want %v", tt.err, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestIsConnectionError(t *testing.T) {
+	tests := []struct {
+		name string
+		err  error
+		want bool
+	}{
+		{"nil", nil, false},
+		{"pg_class_08", &pgconn.PgError{Code: "08003"}, true},
+		{"pg_class_23", &pgconn.PgError{Code: "23505"}, false},
+		{"conn_refused", errors.New("connection refused"), true},
+		{"broken_pipe", errors.New("write: broken pipe"), true},
+		{"generic", errors.New("something else"), false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := IsConnectionError(tt.err); got != tt.want {
+				t.Errorf("IsConnectionError(%v) = %v, want %v", tt.err, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestIsConstraintViolation(t *testing.T) {
+	if IsConstraintViolation(nil) {
+		t.Error("expected false for nil")
+	}
+	if !IsConstraintViolation(&pgconn.PgError{Code: "23505"}) {
+		t.Error("expected true for unique_violation")
+	}
+	if IsConstraintViolation(&pgconn.PgError{Code: "42601"}) {
+		t.Error("expected false for syntax_error")
+	}
+}
+
+func TestPgErrorCode(t *testing.T) {
+	if code := PgErrorCode(errors.New("not pg")); code != "" {
+		t.Errorf("expected empty, got %q", code)
+	}
+	if code := PgErrorCode(&pgconn.PgError{Code: "42P01"}); code != "42P01" {
+		t.Errorf("expected 42P01, got %q", code)
+	}
+}
+
+func TestRetryError(t *testing.T) {
+	inner := errors.New("conn lost")
+	err := newRetryError(3, inner)
+
+	if !errors.Is(err, ErrRetryExhausted) {
+		t.Error("should unwrap to ErrRetryExhausted")
+	}
+	if !errors.Is(err, inner) {
+		t.Error("should unwrap to inner error")
+	}
+	if err.Error() == "" {
+		t.Error("error string should not be empty")
+	}
+}