Fix QgsExpression::dump() for functions without params and for "NOT IN"

And add tests to check if dump() creates an expression that produces the same
result as the original expression.

src/core/qgsexpression.cpp

@@ -2613,7 +2613,7 @@ bool QgsExpression::NodeInOperator::prepare( QgsExpression* parent, const QgsFie
 
 QString QgsExpression::NodeInOperator::dump() const
 {
-  return QString( "%1 IN (%2)" ).arg( mNode->dump() ).arg( mList->dump() );
+  return QString( "%1 %2 IN (%3)" ).arg( mNode->dump() ).arg( mNotIn ? "NOT" : "" ).arg( mList->dump() );
 }
 
 //
@@ -2670,7 +2670,7 @@ QString QgsExpression::NodeFunction::dump() const
 {
   Function* fd = Functions()[mFnIndex];
   if ( fd->params() == 0 )
-    return fd->name(); // special column
+    return QString( "%1%2" ).arg( fd->name() ).arg( fd->name().startsWith( '$' ) ? "" : "()" ); // special column
   else
     return QString( "%1(%2)" ).arg( fd->name() ).arg( mArgs ? mArgs->dump() : QString() ); // function
 }

tests/src/core/testqgsexpression.cpp

@@ -437,13 +437,8 @@ class TestQgsExpression: public QObject
       QTest::newRow( "color cmyka" ) << "color_cmyka(50,25,90,60,200)" << false << QVariant( "51,76,10,200" );
     }
 
-    void evaluation()
+    void run_evaluation_test( QgsExpression& exp, bool evalError, QVariant& result )
     {
-      QFETCH( QString, string );
-      QFETCH( bool, evalError );
-      QFETCH( QVariant, result );
-
-      QgsExpression exp( string );
       QCOMPARE( exp.hasParserError(), false );
       if ( exp.hasParserError() )
         qDebug() << exp.parserErrorString();
@@ -501,6 +496,20 @@ class TestQgsExpression: public QObject
       }
     }
 
+    void evaluation()
+    {
+      QFETCH( QString, string );
+      QFETCH( bool, evalError );
+      QFETCH( QVariant, result );
+
+      QgsExpression exp( string );
+      run_evaluation_test( exp, evalError, result );
+      QgsExpression exp2( exp.dump() );
+      run_evaluation_test( exp2, evalError, result );
+      QgsExpression exp3( exp.expression() );
+      run_evaluation_test( exp3, evalError, result );
+    }
+
     void eval_precedence()
     {
       QCOMPARE( QgsExpression::BinaryOperatorText[QgsExpression::boDiv], "/" );