fix(glossary): handle save errors and improve playlist controls

autotests/glossarystoretest.cpp

@@ -2,6 +2,8 @@
 
 #include "glossarystore.h"
 
+#include <QDir>
+#include <QFile>
 #include <QStandardPaths>
 #include <QTest>
 using namespace Qt::Literals::StringLiterals;
@@ -24,6 +26,36 @@ private Q_SLOTS:
         QCOMPARE(merged.entries.at(0).target, u"Lâm"_s);
         QCOMPARE(merged.entries.at(1).source, u"Sect"_s);
     }
+
+    void saveFailureReturnsError()
+    {
+        QTemporaryDir temp;
+        QVERIFY(temp.isValid());
+        QStandardPaths::setTestModeEnabled(true);
+
+        const QString appData = QStandardPaths::writableLocation(QStandardPaths::AppDataLocation);
+        const QString glossaries = appData + u"/glossaries"_s;
+        QDir(glossaries).removeRecursively();
+        QVERIFY(QDir().mkpath(appData));
+        QFile blocker(glossaries);
+        QVERIFY(blocker.open(QIODevice::WriteOnly));
+        blocker.write("blocked");
+        blocker.close();
+
+        GlossaryStore::Glossary glossary{temp.path(), {{u"Original"_s, u"Translation"_s}}};
+        QString error;
+        QVERIFY(!GlossaryStore::save(glossary, &error));
+        QVERIFY(!error.isEmpty());
+
+        QFile::remove(glossaries);
+    }
+
+    void saveRejectsIncompleteEntry()
+    {
+        QString error;
+        QVERIFY(!GlossaryStore::save({QDir::tempPath(), {{u"Original"_s, {}}}}, &error));
+        QVERIFY(error.contains(u"both"_s));
+    }
 };
 
 QTEST_MAIN(GlossaryStoreTest)