Use fancy C++ strings

The CI doesn't like having too many escaped characters in a normal
string

Author: franzpoeschel

test/CoreTest.cpp

@@ -880,7 +880,7 @@ TEST_CASE( "no_file_ending", "[core]" )
 TEST_CASE( "backend_via_json", "[core]" )
 {
     std::string encodingVariableBased =
-        "{\"backend\": \"json\", \"iteration_encoding\": \"variable_based\"}";
+        R"({"backend": "json", "iteration_encoding": "variable_based"})";
     {
         Series series(
             "../samples/optionsViaJson",
@@ -905,7 +905,7 @@ TEST_CASE( "backend_via_json", "[core]" )
         Series series(
             "../samples/optionsViaJsonOverwritesAutomaticDetection.sst",
             Access::CREATE,
-            "{\"adios2\": {\"engine\": {\"type\": \"bp4\"}}}" );
+            R"({"adios2": {"engine": {"type": "bp4"}}})" );
     }
     REQUIRE( auxiliary::directory_exists(
         "../samples/optionsViaJsonOverwritesAutomaticDetection.bp" ) );
@@ -925,7 +925,7 @@ TEST_CASE( "backend_via_json", "[core]" )
 #endif
 #endif
     std::string encodingFileBased =
-        "{\"backend\": \"json\", \"iteration_encoding\": \"file_based\"}";
+        R"({"backend": "json", "iteration_encoding": "file_based"})";
     {
         /*
          * Should we add JSON options to set the filebased expansion pattern?

test/SerialIOTest.cpp

@@ -3620,7 +3620,7 @@ variableBasedSingleIteration( std::string const & file )
         Series writeSeries(
             file,
             Access::CREATE,
-            "{\"iteration_encoding\": \"variablebased\"}" );
+            R"({\"iteration_encoding\": \"variablebased\"})" );
         REQUIRE(
             writeSeries.iterationEncoding() ==
             IterationEncoding::variableBased );
@@ -4307,7 +4307,7 @@ extendDataset( std::string const & ext )
         Dataset ds1{
             Datatype::INT,
             { 5, 5 },
-            "{ \"resizable\": true, \"resizeble\": \"typo\" }" };
+            R"({ "resizable": true, "resizeble": "typo" })" };
         Dataset ds2{ Datatype::INT, { 10, 5 } };
 
         // array record component -> array record component