Add new obscure qt blog post

content/blog/obscure-qt5.md

@@ -0,0 +1,40 @@
+---
+title: "Obscure Qt: Testing log messages"
+date: 2025-04-15
+draft: false
+tags:
+- Qt
+series:
+- Obscure Qt
+summary: "I noticed that I kept searching for \"how do I check for log messages in Qt tests?\" online. I figure that is a good enough indicator for \"obscure\" and now deserves to be saved on my blog"
+---
+
+I noticed that I kept searching for "how do I check for log messages in Qt tests?" online. I figure that is a good enough indicator for obscurity[^1] and now deserves to be saved on my blog!
+
+The case that spurred this is me writing a bunch of fallible code recently, and I wanted to check if the log message is emitted. Since the message also dynamic, making sure it has the correct line number too. For reference, here is some sample code:
+
+```cpp
+const auto node = childNode.firstChildElement(QStringLiteral("SomeNode"));
+if (node.isNull()) {
+    qWarning() << "Missing <SomeNode> for node at line" << childNode.lineNumber();
+    return std::nullopt;
+}
+...
+```
+
+Checking if this returns `std::nullopt` is easy enough, but what about the log output? It turns out QTest has us covered here with [QTest::ignoreMessage](https://doc.qt.io/qt-6/qtest.html#ignoreMessage). Add it to your test case, and it will panic if the message is not emitted:
+
+```cpp
+QTest::ignoreMessage(QtWarningMsg, "Missing <SomeNode> for node at line 14");
+```
+
+And if the message isn't emitted, it will complain in your test output:
+
+```shell
+INFO   : ConfigFileTest::scaleUpData() Did not receive message: "Missing <SomeNode> for node at line 14"
+FAIL!  : ConfigFileTest::scaleUpData() Not all expected messages were received
+```
+
+However if the message is found, it _hides said message from the test output_ which is extremely useful too. Also useful to know is that there's [a RegExp overload](https://doc.qt.io/qt-6/qtest.html#ignoreMessage-1) if you don't want it to be as specific.
+
+[^1]: Out of pure curiosity, I checked the KDE repositories and there's only ~60 usages of this function. I hope to see more of this the next time I check!