selfpost/internal/logtail/logtail_test.go

package logtail

import (
	"context"
	"errors"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	"testing"
	"time"

	"github.com/mixeme/selfpost/internal/store"
)

func TestParseDelivery(t *testing.T) {
	cases := []struct {
		name                       string
		line                       string
		wantOK                     bool
		queueID, recipient, status string
	}{
		{
			name:      "sent",
			line:      "2026-07-11T11:55:34 host postfix/smtp[26]: 41E862C00D9E: to=<a@example.net>, relay=mx.example.net[203.0.113.9]:25, delay=0.5, dsn=2.0.0, status=sent (250 OK)",
			wantOK:    true,
			queueID:   "41E862C00D9E",
			recipient: "a@example.net",
			status:    store.StatusSent,
		},
		{
			name:      "deferred",
			line:      "host postfix/smtp[26]: 5900C2C00D9E: to=<y@example.net>, relay=none, delay=30, dsn=4.4.1, status=deferred (connect timed out)",
			wantOK:    true,
			queueID:   "5900C2C00D9E",
			recipient: "y@example.net",
			status:    store.StatusDeferred,
		},
		{
			name:      "bounced",
			line:      "host postfix/smtp[26]: ABC: to=<no@example.net>, relay=…, dsn=5.1.1, status=bounced (user unknown)",
			wantOK:    true,
			queueID:   "ABC",
			recipient: "no@example.net",
			status:    store.StatusBounced,
		},
		{
			name:      "expired maps to bounced",
			line:      "host postfix/smtp[26]: DEF: to=<slow@example.net>, relay=none, status=expired (delivery temporarily suspended)",
			wantOK:    true,
			queueID:   "DEF",
			recipient: "slow@example.net",
			status:    store.StatusBounced,
		},
		{
			name:   "qmgr from-line ignored",
			line:   "host postfix/qmgr[10]: 41E862C00D9E: from=<noreply@example.com>, size=500, nrcpt=1 (queue active)",
			wantOK: false,
		},
		{
			name:   "smtpd client-line ignored",
			line:   "host postfix/smtpd[10]: 41E862C00D9E: client=unknown[203.0.113.7]",
			wantOK: false,
		},
		{
			// The remote server's reply is quoted verbatim at the end of the
			// line and is entirely attacker-influenced text. A "status=" that
			// appears in there must not win over the real field, or a bounce
			// would be filed as a success.
			name:      "status= quoted in the remote reply does not win",
			line:      "host postfix/smtp[26]: 9F1A2C00D9E: to=<a@example.net>, relay=mx.example.net[203.0.113.9]:25, dsn=5.1.1, status=bounced (host mx.example.net said: 550 5.1.1 unknown status=sent (in reply to RCPT TO command))",
			wantOK:    true,
			queueID:   "9F1A2C00D9E",
			recipient: "a@example.net",
			status:    store.StatusBounced,
		},
		{
			// Postfix logs the null sender's own delivery (double bounce) with
			// an empty recipient. It parses, and the empty recipient simply
			// matches no send-log row — the panel only ever records mail it
			// accepted from an authenticated client.
			name:      "null recipient parses with an empty address",
			line:      "host postfix/smtp[26]: A1B2C3: to=<>, relay=none, delay=0.1, dsn=2.0.0, status=sent (250 OK)",
			wantOK:    true,
			queueID:   "A1B2C3",
			recipient: "",
			status:    store.StatusSent,
		},
		{
			// An alias/virtual expansion carries orig_to= as well; the address
			// the message was actually delivered to is the one in to=.
			name:      "orig_to is ignored in favour of to",
			line:      "host postfix/lmtp[26]: 4Xk9tS1abcz: to=<real@example.net>, orig_to=<alias@example.net>, relay=x, dsn=2.0.0, status=sent (ok)",
			wantOK:    true,
			queueID:   "4Xk9tS1abcz",
			recipient: "real@example.net",
			status:    store.StatusSent,
		},
		{
			// Postfix's own delivery agents write these two, but neither is a
			// final result we model: "deliverable" comes from address
			// verification probes, and anything unrecognised is dropped rather
			// than guessed at, leaving the row in its previous state.
			name:   "unknown status word is not a delivery result",
			line:   "host postfix/smtp[26]: BEEF01: to=<a@example.net>, relay=x, status=deliverable (ok)",
			wantOK: false,
		},
		{
			name:   "status matching is case-sensitive, as Postfix writes it",
			line:   "host postfix/smtp[26]: BEEF02: to=<a@example.net>, relay=x, dsn=4.0.0, status=Deferred (connect timed out)",
			wantOK: false,
		},
		{
			name:   "cleanup message-id line ignored",
			line:   "host postfix/cleanup[12]: BEEF03: message-id=<x@example.com>",
			wantOK: false,
		},
	}
	for _, c := range cases {
		t.Run(c.name, func(t *testing.T) {
			q, r, s, ok := parseDelivery(c.line)
			if ok != c.wantOK {
				t.Fatalf("ok = %v, want %v", ok, c.wantOK)
			}
			if !ok {
				return
			}
			if q != c.queueID || r != c.recipient || s != c.status {
				t.Fatalf("got (%q,%q,%q), want (%q,%q,%q)", q, r, s, c.queueID, c.recipient, c.status)
			}
		})
	}
}

// captureStore records UpdateStatus calls for the follow integration test and
// keeps the persisted read offset in memory, so a "restart" in a test is a
// second Run against the same captureStore.
type captureStore struct {
	mu    sync.Mutex
	calls []string

	state     store.LogtailState
	haveState bool
	stateErr  error

	// queued is what ListQueuedOlderThan returns, for the reconcile sweep.
	queued    []store.QueuedDelivery
	queuedErr error

	// lines are the log lines kept for messages' pages; pruned is the cutoff of
	// each PruneSendLogLines call.
	lines   []store.SendLogLine
	batches int
	pruned  []time.Time
}

// InsertSendLogLines keeps what the store would: with once, a line is not
// kept a second time under its queue id. batches counts the calls.
func (c *captureStore) InsertSendLogLines(lines []store.SendLogLine, once bool) (int, error) {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.batches++
	wrote := 0
next:
	for _, l := range lines {
		if once {
			for _, have := range c.lines {
				if have.QueueID == l.QueueID && have.Line == l.Line {
					continue next
				}
			}
		}
		c.lines = append(c.lines, l)
		wrote++
	}
	return wrote, nil
}

func (c *captureStore) PruneSendLogLines(cutoff time.Time) (int64, error) {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.pruned = append(c.pruned, cutoff)
	return 0, nil
}

// kept returns the stored lines as "queue-id|line".
func (c *captureStore) kept() []string {
	c.mu.Lock()
	defer c.mu.Unlock()
	out := make([]string, len(c.lines))
	for i, l := range c.lines {
		out[i] = l.QueueID + "|" + l.Line
	}
	return out
}

func (c *captureStore) prunes() int {
	c.mu.Lock()
	defer c.mu.Unlock()
	return len(c.pruned)
}

func (c *captureStore) UpdateStatus(queueID, recipient, status string) (int64, error) {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.calls = append(c.calls, queueID+"|"+recipient+"|"+status)
	return 1, nil
}

func (c *captureStore) DeleteSendLogBefore(time.Time) (int64, error) { return 0, nil }

func (c *captureStore) ListQueuedOlderThan(time.Time) ([]store.QueuedDelivery, error) {
	c.mu.Lock()
	defer c.mu.Unlock()
	return c.queued, c.queuedErr
}

func (c *captureStore) LogtailState(string) (store.LogtailState, bool, error) {
	c.mu.Lock()
	defer c.mu.Unlock()
	if c.stateErr != nil {
		return store.LogtailState{}, false, c.stateErr
	}
	return c.state, c.haveState, nil
}

func (c *captureStore) SaveLogtailState(_ string, st store.LogtailState) error {
	c.mu.Lock()
	defer c.mu.Unlock()
	if c.stateErr != nil {
		return c.stateErr
	}
	c.state, c.haveState = st, true
	return nil
}

func (c *captureStore) snapshot() []string {
	c.mu.Lock()
	defer c.mu.Unlock()
	return append([]string(nil), c.calls...)
}

func (c *captureStore) reset() {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.calls = nil
}

// TestFollowTailsAndRotates writes delivery lines to a log file, then rotates
// it (rename + fresh create, as logrotate does) and writes more, asserting the
// tailer picks up lines from both the original and rotated file.
func TestFollowTailsAndRotates(t *testing.T) {
	old := pollInterval
	pollInterval = 10 * time.Millisecond
	t.Cleanup(func() { pollInterval = old })

	dir := t.TempDir()
	path := filepath.Join(dir, "mail.log")
	if err := os.WriteFile(path, []byte("preexisting line, ignored on start\n"), 0o644); err != nil {
		t.Fatalf("seed log: %v", err)
	}

	cs := &captureStore{}
	ctx, cancel := context.WithCancel(context.Background())
	done := make(chan error, 1)
	go func() { done <- Run(ctx, path, cs, func() int { return 90 }, nil, nil) }()

	// Give follow() time to open at EOF (it seeks to end immediately on start,
	// so the seed line above is ignored), then append a delivery line.
	time.Sleep(50 * time.Millisecond)
	appendLine(t, path, "host postfix/smtp[1]: Q1: to=<a@example.net>, dsn=2.0.0, status=sent (ok)")
	waitFor(t, func() bool { return contains(cs.snapshot(), "Q1|a@example.net|sent") })

	// Rotate: move the current file aside and create a fresh one (logrotate
	// "create"), then append to the new file.
	if err := os.Rename(path, path+".1"); err != nil {
		t.Fatalf("rotate: %v", err)
	}
	if err := os.WriteFile(path, nil, 0o644); err != nil {
		t.Fatalf("recreate: %v", err)
	}
	appendLine(t, path, "host postfix/smtp[1]: Q2: to=<b@example.net>, dsn=5.1.1, status=bounced (nope)")
	waitFor(t, func() bool { return contains(cs.snapshot(), "Q2|b@example.net|bounced") })

	cancel()
	select {
	case <-done:
	case <-time.After(2 * time.Second):
		t.Fatal("Run did not return after cancel")
	}
}

// TestFollowResumesAfterRestart covers the persisted read offset: a restart
// must parse the delivery lines written while the tailer was down (rows that
// would otherwise stay "queued" forever), without re-parsing what it already
// read, and must fall back to reading the whole file when the log was rotated
// or recreated in the meantime.
func TestFollowResumesAfterRestart(t *testing.T) {
	old := pollInterval
	pollInterval = 10 * time.Millisecond
	t.Cleanup(func() { pollInterval = old })

	dir := t.TempDir()
	path := filepath.Join(dir, "mail.log")
	// A head longer than fingerprintSize, so the file stays identifiable across
	// the restart; the lines themselves predate the first start and are ignored.
	seed := strings.Repeat("host postfix/qmgr[1]: seed line, not a delivery\n", 20)
	if err := os.WriteFile(path, []byte(seed), 0o644); err != nil {
		t.Fatalf("seed log: %v", err)
	}

	cs := &captureStore{}
	stop := startRun(t, path, cs)
	appendLine(t, path, "host postfix/smtp[1]: Q1: to=<a@example.net>, dsn=2.0.0, status=sent (ok)")
	waitFor(t, func() bool { return contains(cs.snapshot(), "Q1|a@example.net|sent") })
	stop() // persists the offset past Q1

	// Down: Postfix keeps delivering.
	appendLine(t, path, "host postfix/smtp[1]: Q2: to=<b@example.net>, dsn=2.0.0, status=sent (ok)")

	cs.reset()
	stop = startRun(t, path, cs)
	waitFor(t, func() bool { return contains(cs.snapshot(), "Q2|b@example.net|sent") })
	if contains(cs.snapshot(), "Q1|a@example.net|sent") {
		t.Fatal("resumed run re-parsed Q1: offset was not honoured")
	}
	stop()

	// Down again, and this time the log is replaced (logrotate + fresh create).
	// The stored offset belongs to a file that no longer exists, so the new one
	// must be read from the start.
	if err := os.WriteFile(path, []byte(strings.Repeat("host postfix/qmgr[1]: fresh log after rotation\n", 20)+
		"host postfix/smtp[1]: Q3: to=<c@example.net>, dsn=5.1.1, status=bounced (nope)\n"), 0o644); err != nil {
		t.Fatalf("recreate log: %v", err)
	}

	cs.reset()
	stop = startRun(t, path, cs)
	waitFor(t, func() bool { return contains(cs.snapshot(), "Q3|c@example.net|bounced") })
	stop()
}

// startRun launches the tailer and returns a function that cancels it and waits
// for a clean return, the way a panel restart bookends a run.
func startRun(t *testing.T, path string, cs *captureStore) func() {
	t.Helper()
	ctx, cancel := context.WithCancel(context.Background())
	done := make(chan error, 1)
	go func() { done <- Run(ctx, path, cs, func() int { return 90 }, nil, nil) }()
	// follow() opens and seeks on start; give it a moment before the caller
	// appends, so the append is not raced by the initial open.
	time.Sleep(50 * time.Millisecond)
	return func() {
		t.Helper()
		cancel()
		select {
		case err := <-done:
			if err != nil {
				t.Fatalf("Run: %v", err)
			}
		case <-time.After(2 * time.Second):
			t.Fatal("Run did not return after cancel")
		}
	}
}

func appendLine(t *testing.T, path, line string) {
	t.Helper()
	f, err := os.OpenFile(path, os.O_APPEND|os.O_WRONLY, 0o644)
	if err != nil {
		t.Fatalf("open for append: %v", err)
	}
	defer f.Close()
	if _, err := f.WriteString(line + "\n"); err != nil {
		t.Fatalf("append: %v", err)
	}
}

func contains(ss []string, want string) bool {
	for _, s := range ss {
		if s == want {
			return true
		}
	}
	return false
}

func waitFor(t *testing.T, cond func() bool) {
	t.Helper()
	deadline := time.Now().Add(2 * time.Second)
	for time.Now().Before(deadline) {
		if cond() {
			return
		}
		time.Sleep(5 * time.Millisecond)
	}
	t.Fatal("condition not met within timeout")
}

// stubQueue makes the reconcile sweep answer from a fixed list of queue ids
// instead of a running Postfix, or fail if err is non-nil.
func stubQueue(t *testing.T, err error, ids ...string) *int {
	t.Helper()
	calls := 0
	old := queueIDs
	queueIDs = func() (map[string]struct{}, error) {
		calls++
		if err != nil {
			return nil, err
		}
		set := make(map[string]struct{}, len(ids))
		for _, id := range ids {
			set[id] = struct{}{}
		}
		return set, nil
	}
	t.Cleanup(func() { queueIDs = old })
	return &calls
}

// A row stays "queued" forever when its delivery lines are gone for good. The
// queue is what settles it: a message Postfix still holds is simply in flight
// and must be left alone, while one it no longer holds will never be reported
// on and is closed.
func TestReconcileClosesOnlyWhatPostfixNoLongerHolds(t *testing.T) {
	stubQueue(t, nil, "STILLQ")

	cs := &captureStore{queued: []store.QueuedDelivery{
		{QueueID: "STILLQ", To: "inflight@example.net"},
		{QueueID: "GONEQ", To: "lost@example.net"},
	}}
	reconcile(cs, time.Now().UTC())

	got := cs.snapshot()
	if len(got) != 1 || got[0] != "GONEQ|lost@example.net|"+store.StatusBounced {
		t.Fatalf("got %v, want only the message Postfix dropped closed as bounced", got)
	}
}

// A queue that cannot be listed says nothing about any message — treating the
// failure as an empty queue would close every stale row at once.
func TestReconcileLeavesRowsAloneWhenTheQueueCannotBeRead(t *testing.T) {
	stubQueue(t, errors.New("postqueue: Permission denied"))

	cs := &captureStore{queued: []store.QueuedDelivery{
		{QueueID: "GONEQ", To: "lost@example.net"},
	}}
	reconcile(cs, time.Now().UTC())

	if got := cs.snapshot(); len(got) != 0 {
		t.Fatalf("got %v, want no row touched", got)
	}
}

// With nothing stale to explain there is no reason to shell out to postqueue at
// all — which is the normal state of a relay that is keeping up.
func TestReconcileSkipsTheQueueWhenNoRowIsStuck(t *testing.T) {
	calls := stubQueue(t, nil)

	reconcile(&captureStore{}, time.Now().UTC())

	if *calls != 0 {
		t.Fatalf("queue listed %d time(s), want none", *calls)
	}
}

// A delivery's page shows what Postfix wrote about that one message, so the
// read has to pick its queue-id's lines out of everything else the mail path
// logged around them — and only its own: queue ids are hexadecimal runs, and a
// shorter one is regularly the tail of a longer one.
func TestQueueLinesPicksOutOneMessage(t *testing.T) {
	path := writeLog(t,
		"host postfix/smtpd[20]: 41E862C00D9E: client=mail.example.com[203.0.113.4]",
		"host postfix/qmgr[10]: 5900C2C00D9E: from=<other@example.com>, size=500, nrcpt=1 (queue active)",
		"host postfix/cleanup[15]: 41E862C00D9E: message-id=<abc@example.com>",
		// Same run of characters, longer id: not this message.
		"host postfix/smtp[26]: FF41E862C00D9E: to=<z@example.net>, status=sent (250 OK)",
		"host opendkim[30]: 41E862C00D9E: DKIM-Signature field added (s=mail d=example.com)",
		"host postfix/smtp[26]: 41E862C00D9E: to=<a@example.net>, relay=mx.example.net[203.0.113.9]:25, dsn=2.0.0, status=sent (250 OK)",
	)

	lines, err := QueueLines(path, "41E862C00D9E", 200)
	if err != nil {
		t.Fatalf("QueueLines: %v", err)
	}
	if len(lines) != 4 {
		t.Fatalf("got %d lines, want 4:\n%s", len(lines), strings.Join(lines, "\n"))
	}
	// Oldest first: the page reads the message's history downwards.
	if !strings.Contains(lines[0], "client=") || !strings.Contains(lines[3], "status=sent") {
		t.Errorf("lines are not in the order they were logged:\n%s", strings.Join(lines, "\n"))
	}
	for _, line := range lines {
		if strings.Contains(line, "FF41E862C00D9E") || strings.Contains(line, "5900C2C00D9E") {
			t.Errorf("another message's line came back: %q", line)
		}
	}
}

// A message the milter refused has no queue id, so there is nothing to match
// on — every line in the log would be someone else's.
func TestQueueLinesWithoutAQueueIDMatchesNothing(t *testing.T) {
	path := writeLog(t, "host postfix/smtp[26]: 41E862C00D9E: to=<a@example.net>, status=sent (250 OK)")

	lines, err := QueueLines(path, "", 200)
	if err != nil {
		t.Fatalf("QueueLines: %v", err)
	}
	if lines != nil {
		t.Errorf("got %v, want no lines", lines)
	}
}

// The cap keeps the newest lines, not the first ones: what a message did last
// is what its page is opened for.
func TestQueueLinesCapKeepsTheLatest(t *testing.T) {
	var log []string
	for i := 0; i < 10; i++ {
		log = append(log, "host postfix/smtp[26]: ABC123: attempt "+itoa(i))
	}
	path := writeLog(t, log...)

	lines, err := QueueLines(path, "ABC123", 3)
	if err != nil {
		t.Fatalf("QueueLines: %v", err)
	}
	if len(lines) != 3 || !strings.HasSuffix(lines[0], "attempt 7") || !strings.HasSuffix(lines[2], "attempt 9") {
		t.Errorf("cap did not keep the last three:\n%s", strings.Join(lines, "\n"))
	}
}

// Send-log rows outlive mail.log — retention is ninety days and rotation keeps
// fourteen files — so a message whose lines are gone, or a log that is between
// rotations and absent altogether, is an empty answer for the page to explain,
// not an error for it to report.
func TestQueueLinesOnAMessageWithNoLinesLeft(t *testing.T) {
	path := writeLog(t, "host postfix/smtp[26]: 5900C2C00D9E: to=<z@example.net>, status=sent (250 OK)")

	lines, err := QueueLines(path, "41E862C00D9E", 200)
	if err != nil {
		t.Fatalf("QueueLines: %v", err)
	}
	if lines != nil {
		t.Errorf("got %v, want no lines", lines)
	}
}

// writeLog creates a mail.log holding the given lines and returns its path.
func writeLog(t *testing.T, lines ...string) string {
	t.Helper()
	path := filepath.Join(t.TempDir(), "mail.log")
	body := ""
	for _, line := range lines {
		body += line + "\n"
	}
	if err := os.WriteFile(path, []byte(body), 0o644); err != nil {
		t.Fatalf("write log: %v", err)
	}
	return path
}

func itoa(n int) string { return strconv.Itoa(n) }

// The read is bounded, so on a log that has grown all day it starts in the
// middle of a line. That fragment is not a line and must not come back as one,
// and anything before the budget is out of reach — which the page reports the
// same way as a message whose lines have rotated away.
func TestQueueLinesReadsABoundedTail(t *testing.T) {
	old := queueScanBytes
	queueScanBytes = 120
	t.Cleanup(func() { queueScanBytes = old })

	path := writeLog(t,
		"host postfix/smtp[26]: ABC123: too far back to reach, padded out past the budget with this run of filler text",
		"host postfix/smtp[26]: ABC123: within the budget",
	)

	lines, err := QueueLines(path, "ABC123", 200)
	if err != nil {
		t.Fatalf("QueueLines: %v", err)
	}
	if len(lines) != 1 || !strings.HasSuffix(lines[0], "within the budget") {
		t.Errorf("got %d lines, want only the one inside the budget:\n%s", len(lines), strings.Join(lines, "\n"))
	}
}

// The delivery page shows a message's lines as a table of when and what, so the
// timestamp has to come off the head of the line — in either of the two formats
// a mail log arrives in — and nothing may be lost doing it.
func TestSplitTimestamp(t *testing.T) {
	cases := []struct {
		name        string
		line        string
		stamp, rest string
	}{
		{
			name:  "RFC 3339, which maillog_file_format selects on Postfix 3.9 and up",
			line:  "2026-08-03T05:15:52.219218+00:00 mail postfix/smtp[26]: 4A1B2C3D: to=<a@example.net>, status=sent (250 OK)",
			stamp: "2026-08-03 05:15:52",
			rest:  "mail postfix/smtp[26]: 4A1B2C3D: to=<a@example.net>, status=sent (250 OK)",
		},
		{
			name:  "no fractional seconds, zone as Z",
			line:  "2026-08-03T05:15:52Z mail postfix/qmgr[10]: 4A1B2C3D: removed",
			stamp: "2026-08-03 05:15:52",
			rest:  "mail postfix/qmgr[10]: 4A1B2C3D: removed",
		},
		{
			name:  "no zone at all",
			line:  "2026-08-03T05:15:52 mail opendkim[30]: 4A1B2C3D: DKIM-Signature field added",
			stamp: "2026-08-03 05:15:52",
			rest:  "mail opendkim[30]: 4A1B2C3D: DKIM-Signature field added",
		},
		{
			name:  "syslog's traditional format, space-padded day",
			line:  "Aug  3 05:15:52 mail postfix/smtpd[20]: 4A1B2C3D: client=app.example.ru[203.0.113.4]",
			stamp: "Aug  3 05:15:52",
			rest:  "mail postfix/smtpd[20]: 4A1B2C3D: client=app.example.ru[203.0.113.4]",
		},
		{
			// Copied off the live relay (Postfix 3.7, which has no
			// maillog_file_format), so this is the shape the panel actually
			// meets: zero-padded day, and the host is the container's name.
			name:  "syslog's traditional format as the live relay writes it",
			line:  "Aug 08 07:26:41 selfpost postfix/master[231]: daemon started -- version 3.7.11, configuration /etc/postfix",
			stamp: "Aug 08 07:26:41",
			rest:  "selfpost postfix/master[231]: daemon started -- version 3.7.11, configuration /etc/postfix",
		},
		{
			name:  "unrecognised head keeps the whole line",
			line:  "mail postfix/smtp[26]: 4A1B2C3D: to=<a@example.net>, status=sent (250 OK)",
			stamp: "",
			rest:  "mail postfix/smtp[26]: 4A1B2C3D: to=<a@example.net>, status=sent (250 OK)",
		},
		{
			// A date-like run that is not the head of the line is not a stamp.
			name:  "date inside the text is left alone",
			line:  "mail postfix/smtp[26]: ABC: 220 mx.example.net ready at 2026-08-03T05:15:52+00:00",
			stamp: "",
			rest:  "mail postfix/smtp[26]: ABC: 220 mx.example.net ready at 2026-08-03T05:15:52+00:00",
		},
	}
	for _, c := range cases {
		t.Run(c.name, func(t *testing.T) {
			stamp, rest := SplitTimestamp(c.line)
			if stamp != c.stamp || rest != c.rest {
				t.Errorf("SplitTimestamp(%q) = (%q, %q), want (%q, %q)", c.line, stamp, rest, c.stamp, c.rest)
			}
			// Whatever the split, the line's own text survives it whole.
			if !strings.Contains(c.line, rest) {
				t.Errorf("the text column is not part of the line it came from: %q", rest)
			}
		})
	}
}