Initial commit: stalwart-migrator design and scaffolding

In-place upgrade tool for Stalwart Mail Server (0.15.5 -> latest) with
checkpointed rollback and post-migration validation. Design stage; see
ARCHITECTURE.md.

internal/backup/sqlbackup_test.go

@@ -0,0 +1,85 @@
+package backup
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestBuildPgDumpArgs(t *testing.T) {
+	args := BuildPgDumpArgs(SQLOptions{
+		Host: "db.internal", Port: "5432", Database: "stalwart", User: "stalwart", OutPath: "/backups/out.sql",
+	})
+	joined := strings.Join(args, " ")
+	for _, want := range []string{"-U stalwart", "-d stalwart", "-h db.internal", "-p 5432", "-f /backups/out.sql"} {
+		if !strings.Contains(joined, want) {
+			t.Errorf("BuildPgDumpArgs = %q, missing %q", joined, want)
+		}
+	}
+	for _, table := range criticalTables {
+		if !strings.Contains(joined, "-t "+table) {
+			t.Errorf("BuildPgDumpArgs missing critical table flag for %q: %q", table, joined)
+		}
+	}
+}
+
+func TestBuildMySQLDumpArgs(t *testing.T) {
+	args := BuildMySQLDumpArgs(SQLOptions{Host: "db.internal", Port: "3306", Database: "stalwart", User: "stalwart"})
+	joined := strings.Join(args, " ")
+	if !strings.Contains(joined, "-u stalwart") || !strings.Contains(joined, "-h db.internal") || !strings.Contains(joined, "-P 3306") {
+		t.Errorf("BuildMySQLDumpArgs = %q, missing expected flags", joined)
+	}
+	if !strings.HasSuffix(joined, strings.Join(criticalTables, " ")) {
+		t.Errorf("BuildMySQLDumpArgs = %q, want it to end with the critical table list", joined)
+	}
+}
+
+func TestRunPgDumpInvokesPgDumpWithArgs(t *testing.T) {
+	dir := t.TempDir()
+	log := argsFile(t, dir)
+	withFakeExecutable(t, "pg_dump", fakeScriptLoggingArgs(log, "exit 0"))
+
+	err := RunPgDump(context.Background(), SQLOptions{
+		User: "stalwart", Database: "stalwart", OutPath: filepath.Join(dir, "out.sql"),
+	})
+	if err != nil {
+		t.Fatalf("RunPgDump: %v", err)
+	}
+	got := readArgsFile(t, log)
+	if !strings.Contains(got, "-U stalwart") {
+		t.Errorf("pg_dump was invoked with %q, missing -U stalwart", got)
+	}
+}
+
+func TestRunPgDumpPropagatesFailure(t *testing.T) {
+	dir := t.TempDir()
+	withFakeExecutable(t, "pg_dump", "#!/bin/sh\necho 'connection refused' >&2\nexit 1\n")
+
+	err := RunPgDump(context.Background(), SQLOptions{User: "stalwart", Database: "stalwart", OutPath: filepath.Join(dir, "out.sql")})
+	if err == nil {
+		t.Fatal("RunPgDump should have returned an error when pg_dump exits non-zero")
+	}
+	if !strings.Contains(err.Error(), "connection refused") {
+		t.Errorf("error = %v, want it to include pg_dump's stderr", err)
+	}
+}
+
+func TestRunMySQLDumpWritesStdoutToOutPath(t *testing.T) {
+	dir := t.TempDir()
+	withFakeExecutable(t, "mysqldump", "#!/bin/sh\necho '-- fake dump output'\n")
+
+	outPath := filepath.Join(dir, "out.sql")
+	err := RunMySQLDump(context.Background(), SQLOptions{User: "stalwart", Database: "stalwart", OutPath: outPath})
+	if err != nil {
+		t.Fatalf("RunMySQLDump: %v", err)
+	}
+	data, err := os.ReadFile(outPath)
+	if err != nil {
+		t.Fatalf("ReadFile: %v", err)
+	}
+	if !strings.Contains(string(data), "fake dump output") {
+		t.Errorf("out.sql = %q, want fake dump output redirected into it", data)
+	}
+}