1 files changed, 180 insertions, 0 deletions
diff --git a/tests/test_syncmonitor.cpp b/tests/test_syncmonitor.cpp
new file mode 100644
index 0000000..c120085
--- /dev/null
+++ b/tests/test_syncmonitor.cpp
@@ -0,0 +1,180 @@
+/*
+ * qtmaildir - a Qt6 mail client for notmuch-indexed Maildirs
+ * Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include <QtTest>
+
+#include <QSignalSpy>
+#include <QTemporaryDir>
+#include <QTemporaryFile>
+
+#include "syncmonitor.h"
+
+/// SyncMonitor answers one question: is a sync running that this process did
+/// not start? The parsing of /proc/locks is the testable part and is kept
+/// separate from the polling for exactly that reason.
+class TestSyncMonitor : public QObject
+{
+    Q_OBJECT
+private slots:
+    void anFlockOnTheWatchedInodeIsHeld();
+    void anFlockOnAnotherInodeIsIgnored();
+    void aPosixLockOnTheWatchedInodeIsIgnored();
+    void emptyContentMeansNotHeld();
+    void garbageLinesAreSkippedRatherThanMisread();
+    void anUnreadableLockTableIsUnknownNotIdle();
+    void aMissingLockFileIsNotHeld();
+    void theStateChangeSignalFiresOnlyOnTransitions();
+};
+
+void TestSyncMonitor::anFlockOnTheWatchedInodeIsHeld()
+{
+    // The real shape of a held lock, taken verbatim from /proc/locks while
+    // mailsync.sh held /tmp/mbsync.lock: the inode is the last colon-separated
+    // field of the device:inode column, not the whole column.
+    const QString content =
+        QStringLiteral("82: FLOCK  ADVISORY  WRITE 9051 fc:00:12058676 0 EOF\n");
+    QVERIFY(SyncMonitor::lockHeldIn(content, 12058676));
+}
+
+void TestSyncMonitor::anFlockOnAnotherInodeIsIgnored()
+{
+    // A busy machine has many flocks. Matching anything but our own inode would
+    // report a sync whenever some unrelated program took a lock.
+    const QString content =
+        QStringLiteral("82: FLOCK  ADVISORY  WRITE 9051 fc:00:99999999 0 EOF\n");
+    QVERIFY(!SyncMonitor::lockHeldIn(content, 12058676));
+}
+
+void TestSyncMonitor::aPosixLockOnTheWatchedInodeIsIgnored()
+{
+    // flock(2) and fcntl(2) are separate namespaces in the kernel and cannot
+    // see each other; mailsync.sh uses flock(2). A POSIX lock on the same file
+    // is somebody else's, and treating it as ours would report a sync that is
+    // not running. Verified: fcntl(F_OFD_GETLK) reports UNLOCKED against a
+    // held flock, which is why this distinction is not academic.
+    const QString content =
+        QStringLiteral("1: POSIX  ADVISORY  WRITE 1234 fc:00:12058676 0 EOF\n");
+    QVERIFY(!SyncMonitor::lockHeldIn(content, 12058676));
+}
+
+void TestSyncMonitor::emptyContentMeansNotHeld()
+{
+    QVERIFY(!SyncMonitor::lockHeldIn(QString(), 12058676));
+}
+
+void TestSyncMonitor::garbageLinesAreSkippedRatherThanMisread()
+{
+    // /proc/locks gains fields across kernel versions, and a line can be
+    // truncated as it is read. A short line must not match by accident, and
+    // must not stop the lines after it from being read.
+    const QString content = QStringLiteral(
+        "not a lock line at all\n"
+        "3: FLOCK\n"
+        "82: FLOCK  ADVISORY  WRITE 9051 fc:00:12058676 0 EOF\n");
+    QVERIFY(SyncMonitor::lockHeldIn(content, 12058676));
+
+    const QString onlyGarbage = QStringLiteral("nonsense\n3: FLOCK\n");
+    QVERIFY(!SyncMonitor::lockHeldIn(onlyGarbage, 12058676));
+}
+
+void TestSyncMonitor::anUnreadableLockTableIsUnknownNotIdle()
+{
+    // /proc/locks is Linux-only. Where it cannot be read the honest answer is
+    // "unknown", and the indicator stays hidden. Reporting idle would be a
+    // claim the monitor cannot support, and it is the claim that matters:
+    // "no sync is running" is what lets the window quit.
+    SyncMonitor monitor(QStringLiteral("/nonexistent/mbsync.lock"),
+                        QStringLiteral("/nonexistent/proc/locks"));
+    QCOMPARE(monitor.state(), SyncMonitor::State::Unknown);
+    monitor.poll();
+    QCOMPARE(monitor.state(), SyncMonitor::State::Unknown);
+}
+
+void TestSyncMonitor::aMissingLockFileIsNotHeld()
+{
+    // Before the first sync ever runs there is no lock file. That is not a
+    // sync in progress, and it must not read as unknown either: the lock table
+    // is perfectly readable, there is simply nothing holding anything.
+    QTemporaryDir dir;
+    QVERIFY(dir.isValid());
+
+    QTemporaryFile locks;
+    QVERIFY(locks.open());
+    locks.write("82: FLOCK  ADVISORY  WRITE 9051 fc:00:12058676 0 EOF\n");
+    locks.flush();
+
+    SyncMonitor monitor(dir.filePath(QStringLiteral("never-created.lock")),
+                        locks.fileName());
+    monitor.poll();
+    QCOMPARE(monitor.state(), SyncMonitor::State::Idle);
+}
+
+void TestSyncMonitor::theStateChangeSignalFiresOnlyOnTransitions()
+{
+    // The UI reacts to a sync starting and finishing, so a signal on every
+    // poll would repaint the status bar every two seconds forever and would
+    // stamp over whatever else had been written there.
+    QTemporaryDir dir;
+    QVERIFY(dir.isValid());
+    const QString lockPath = dir.filePath(QStringLiteral("mbsync.lock"));
+    {
+        QFile lock(lockPath);
+        QVERIFY(lock.open(QIODevice::WriteOnly));
+    }
+
+    const qint64 inode = SyncMonitor::inodeOf(lockPath);
+    QVERIFY(inode > 0);
+
+    // A stand-in for /proc/locks whose contents the test controls.
+    const QString locksPath = dir.filePath(QStringLiteral("locks"));
+    auto writeLocks = [&locksPath](const QString &text) {
+        QFile f(locksPath);
+        QVERIFY(f.open(QIODevice::WriteOnly | QIODevice::Truncate));
+        f.write(text.toUtf8());
+    };
+    writeLocks(QString());
+
+    SyncMonitor monitor(lockPath, locksPath);
+    QSignalSpy spy(&monitor, &SyncMonitor::stateChanged);
+
+    monitor.poll();
+    QCOMPARE(monitor.state(), SyncMonitor::State::Idle);
+    QCOMPARE(spy.count(), 1);   // Unknown -> Idle is a real transition.
+
+    monitor.poll();
+    monitor.poll();
+    QCOMPARE(spy.count(), 1);   // Still idle: no further signals.
+
+    writeLocks(QStringLiteral("82: FLOCK  ADVISORY  WRITE 9051 fc:00:%1 0 EOF\n")
+                   .arg(inode));
+    monitor.poll();
+    QCOMPARE(monitor.state(), SyncMonitor::State::Running);
+    QCOMPARE(spy.count(), 2);
+
+    monitor.poll();
+    QCOMPARE(spy.count(), 2);   // Still running.
+
+    writeLocks(QString());
+    monitor.poll();
+    QCOMPARE(monitor.state(), SyncMonitor::State::Idle);
+    QCOMPARE(spy.count(), 3);
+}
+
+QTEST_MAIN(TestSyncMonitor)
+
+#include "test_syncmonitor.moc"