doc: Explain QT_QPA_PLATFORM for gui tests

Author: MarcoFalke

src/qt/test/addressbooktests.cpp

@@ -146,7 +146,7 @@ void AddressBookTests::addressBookTests()
         // and fails to handle returned nulls
         // (https://bugreports.qt.io/browse/QTBUG-49686).
         QWARN("Skipping AddressBookTests on mac build with 'minimal' platform set due to Qt bugs. To run AppTests, invoke "
-              "with 'test_bitcoin-qt -platform cocoa' on mac, or else use a linux or windows build.");
+              "with 'QT_QPA_PLATFORM=cocoa test_bitcoin-qt' on mac, or else use a linux or windows build.");
         return;
     }
 #endif

src/qt/test/apptests.cpp

@@ -57,7 +57,7 @@ void AppTests::appTests()
         // and fails to handle returned nulls
         // (https://bugreports.qt.io/browse/QTBUG-49686).
         QWARN("Skipping AppTests on mac build with 'minimal' platform set due to Qt bugs. To run AppTests, invoke "
-              "with 'test_bitcoin-qt -platform cocoa' on mac, or else use a linux or windows build.");
+              "with 'QT_QPA_PLATFORM=cocoa test_bitcoin-qt' on mac, or else use a linux or windows build.");
         return;
     }
 #endif

src/qt/test/test_main.cpp

@@ -63,7 +63,7 @@ int main(int argc, char *argv[])
     #if defined(WIN32)
         _putenv_s("QT_QPA_PLATFORM", "minimal");
     #else
-        setenv("QT_QPA_PLATFORM", "minimal", 0);
+        setenv("QT_QPA_PLATFORM", "minimal", /* overwrite */ 0);
     #endif
 
     // Don't remove this, it's needed to access

src/qt/test/wallettests.cpp

@@ -123,9 +123,9 @@ void BumpFee(TransactionView& view, const uint256& txid, bool expectDisabled, st
 //
 // This also requires overriding the default minimal Qt platform:
 //
-//     src/qt/test/test_bitcoin-qt -platform xcb      # Linux
-//     src/qt/test/test_bitcoin-qt -platform windows  # Windows
-//     src/qt/test/test_bitcoin-qt -platform cocoa    # macOS
+//     QT_QPA_PLATFORM=xcb     src/qt/test/test_bitcoin-qt  # Linux
+//     QT_QPA_PLATFORM=windows src/qt/test/test_bitcoin-qt  # Windows
+//     QT_QPA_PLATFORM=cocoa   src/qt/test/test_bitcoin-qt  # macOS
 void TestGUI()
 {
     // Set up wallet and chain with 105 blocks (5 mature blocks for spending).
@@ -256,7 +256,7 @@ void WalletTests::walletTests()
         // and fails to handle returned nulls
         // (https://bugreports.qt.io/browse/QTBUG-49686).
         QWARN("Skipping WalletTests on mac build with 'minimal' platform set due to Qt bugs. To run AppTests, invoke "
-              "with 'test_bitcoin-qt -platform cocoa' on mac, or else use a linux or windows build.");
+              "with 'QT_QPA_PLATFORM=cocoa test_bitcoin-qt' on mac, or else use a linux or windows build.");
         return;
     }
 #endif