Store singular TestRunNode in CumulativeReporterBase

There can never be more than one, so there is no reason to provide
genericity over multiple nodes.

src/catch2/reporters/catch_reporter_cumulative_base.cpp

@@ -100,8 +100,9 @@ namespace Catch {
 
 
     void CumulativeReporterBase::testRunEnded( TestRunStats const& testRunStats ) {
-        m_testRuns.emplace_back( testRunStats );
-        m_testRuns.back().children.swap( m_testCases );
+        assert(!m_testRun && "CumulativeReporterBase assumes there can only be one test run");
+        m_testRun = Detail::make_unique<TestRunNode>( testRunStats );
+        m_testRun->children.swap( m_testCases );
         testRunEndedCumulative();
     }
 

src/catch2/reporters/catch_reporter_cumulative_base.hpp

@@ -73,10 +73,11 @@ namespace Catch {
 
         std::ostream& stream;
         // Note: We rely on pointer identity being stable, which is why
-        //       which is why we store around pointers rather than values.
+        //       we store pointers to the nodes rather than the values.
         std::vector<Detail::unique_ptr<TestCaseNode>> m_testCases;
-
-        std::vector<TestRunNode> m_testRuns;
+        // We need lazy construction here. We should probably refactor it
+        // later, after the events are redone.
+        Detail::unique_ptr<TestRunNode> m_testRun;
 
         Detail::unique_ptr<SectionNode> m_rootSection;
         SectionNode* m_deepestSection = nullptr;

src/catch2/reporters/catch_reporter_junit.cpp

@@ -99,10 +99,7 @@ namespace Catch {
 
     void JunitReporter::testRunEndedCumulative() {
         const auto suiteTime = suiteTimer.getElapsedSeconds();
-        // HACK: There can only be one testRunNode? This needs to be
-        //       refactored after the group nodes are excised.
-        assert(m_testRuns.size() == 1);
-        writeRun( m_testRuns.back(), suiteTime );
+        writeRun( *m_testRun, suiteTime );
         xml.endElement();
     }
 

src/catch2/reporters/catch_reporter_sonarqube.hpp

@@ -35,10 +35,7 @@ namespace Catch {
         void testRunStarting( TestRunInfo const& testRunInfo ) override;
 
         void testRunEndedCumulative() override {
-            // HACK: There can only be one testRunNode? This needs to be
-            //       refactored after the group nodes are excised.
-            assert( m_testRuns.size() == 1 );
-            writeRun( m_testRuns.back() );
+            writeRun( *m_testRun );
             xml.endElement();
         }