Merge bitcoin-core/gui#335: test: Use QSignalSpy instead of QEventLoop

7eea659 qt, test: use qsignalspy instead of qeventloop (Jarol Rodriguez)

Pull request description:

  This PR refactors our GUI `apptests` to use [QSignalSpy](https://doc.qt.io/qt-5/qsignalspy.html) instead of [QEventLoop](https://doc.qt.io/qt-5/qeventloop.html).

  `QSignalSpy` is more appropriate for our GUI test's as it is purpose-built for testing emission of signals and sets up its own `QEventLoop` when the `wait` function is called.

ACKs for top commit:
  hebasto:
    ACK 7eea659, tested on Linux Mint 20.1 (Qt 5.12.8).
  promag:
    Code review ACK 7eea659.

Tree-SHA512: 3adddbcc5efd726302b606980c9923025c44bb8ee16cb8a183e633e423179c0822db66de9ccba20dc5124fff34af4151a379c9cd18130625c60789ce809ee6fd

Author: hebasto

src/qt/test/apptests.cpp

@@ -20,10 +20,10 @@
 #endif
 
 #include <QAction>
-#include <QEventLoop>
 #include <QLineEdit>
 #include <QScopedPointer>
 #include <QSettings>
+#include <QSignalSpy>
 #include <QTest>
 #include <QTextEdit>
 #include <QtGlobal>
@@ -34,13 +34,14 @@ namespace {
 //! Call getblockchaininfo RPC and check first field of JSON output.
 void TestRpcCommand(RPCConsole* console)
 {
-    QEventLoop loop;
     QTextEdit* messagesWidget = console->findChild<QTextEdit*>("messagesWidget");
-    QObject::connect(messagesWidget, &QTextEdit::textChanged, &loop, &QEventLoop::quit);
     QLineEdit* lineEdit = console->findChild<QLineEdit*>("lineEdit");
+    QSignalSpy mw_spy(messagesWidget, &QTextEdit::textChanged);
+    QVERIFY(mw_spy.isValid());
     QTest::keyClicks(lineEdit, "getblockchaininfo");
     QTest::keyClick(lineEdit, Qt::Key_Return);
-    loop.exec();
+    QVERIFY(mw_spy.wait(1000));
+    QCOMPARE(mw_spy.count(), 2);
     QString output = messagesWidget->toPlainText();
     UniValue value;
     value.read(output.right(output.size() - output.indexOf("{")).toStdString());