test: stop two tests depending on the machine they run on

Both are the same class of defect: a test that reads real machine state and
so passes or fails on circumstance rather than on the code under test.

Item 38. Every MainWindow a test builds constructed its SyncMonitor on the
live /proc/locks, so a window observed the machine's actual sync state and
the sync-button assertion failed whenever the user's cron sync happened to
be running. Cron fires every ten minutes and a run lasts ~35s, which is
roughly 6% of runs, and it read as flakiness. SyncMonitor already took an
injectable locks path for exactly this; MainWindow did not expose it. It
does now, as a test seam rather than a config key: /proc/locks is not
something a user would set, and a wrong value silently disables background
sync detection instead of failing loudly.

The monitor is still constructed and started, per the item's own constraint.
Only the table it reads is redirected, to an empty file in the test's own
temporary directory.

Item 46. uiStateSurvivesARestart asserted a 940px width, and the offscreen
platform reports an 800x800 screen. restoreGeometry() clamps to the
available area, so the width came back as 798 while the 620 height, which
fits, restored untouched. That asymmetry was the tell that persistence was
fine and the test was wrong. The size is now 640x560 and carries no meaning
beyond differing from the default.

Verified by reproducing the original conditions rather than by waiting for
them: the suite run under flock -n /tmp/mbsync.lock fails item 38's
assertion with the seam bypassed and passes with it in place, and item 46
now passes under offscreen where it failed. One dud mutation is recorded in
the backlog, writing an unparseable line into the injected lock table does
not fail the test, because lockHeldIn() correctly finds no lock in it.

Suite: 15/15 offscreen with the lock held, and green on Wayland except the
pre-existing querycompleter screenshot flake, which fails to grab under
Wayland and passes offscreen.

2 files changed, 28 insertions, 1 deletions

diff --git a/src/mainwindow.cpp b/src/mainwindow.cpp
index 7c7b801..75549d3 100644
--- a/src/mainwindow.cpp
+++ b/src/mainwindow.cpp
@@ -83,6 +83,21 @@ QString MainWindow::uiStatePath()
     return base + QStringLiteral("/qtmaildir/uistate.conf");
 }
 
+namespace {
+/// Overridden only by setLocksPathForTesting(); "/proc/locks" in every real run.
+QString g_locksPath = QStringLiteral("/proc/locks");
+} // namespace
+
+void MainWindow::setLocksPathForTesting(const QString &path)
+{
+    g_locksPath = path;
+}
+
+QString MainWindow::locksPath()
+{
+    return g_locksPath;
+}
+
 void MainWindow::restoreUiState()
 {
     QSettings state(uiStatePath(), QSettings::IniFormat);
@@ -465,7 +480,7 @@ void MainWindow::buildUi()
     // every ten minutes, so mail arrives and tags change while the window sits
     // idle, and until now nothing here noticed.
     m_syncMonitor = new SyncMonitor(SyncMonitor::defaultLockPath(),
-                                    QStringLiteral("/proc/locks"), this);
+                                    locksPath(), this);
     connect(m_syncMonitor, &SyncMonitor::stateChanged,
             this, &MainWindow::onExternalSyncStateChanged);
     m_syncMonitor->start();
diff --git a/src/mainwindow.h b/src/mainwindow.h
index 22c8187..96b27f4 100644
--- a/src/mainwindow.h
+++ b/src/mainwindow.h
@@ -104,6 +104,18 @@ public:
     /// preserve comments or key order).
     static QString uiStatePath();
 
+    /// Kernel lock table every MainWindow's SyncMonitor watches, "/proc/locks"
+    /// unless a test overrides it.
+    ///
+    /// A test seam, deliberately NOT a config key: /proc/locks is not something
+    /// a user would ever set, and a wrong value silently disables background
+    /// sync detection rather than failing loudly. Without this every window a
+    /// test builds observes the machine's real sync state, so a test asserting
+    /// on the sync button fails whenever the user's cron sync happens to be
+    /// running (item 38).
+    static void setLocksPathForTesting(const QString &path);
+    static QString locksPath();
+
 protected:
     void closeEvent(QCloseEvent *event) override;