Replaced InvalidGridException with a logger warning

src/main/java/edu/ie3/datamodel/models/input/container/JointGridContainer.java

@@ -5,16 +5,19 @@
 */
 package edu.ie3.datamodel.models.input.container;
 
-import edu.ie3.datamodel.exceptions.InvalidGridException;
 import edu.ie3.datamodel.graph.SubGridTopologyGraph;
 import edu.ie3.datamodel.utils.ContainerUtils;
 import java.util.Objects;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /** Model class to hold input models for more than one galvanically separated subnet */
 public class JointGridContainer extends GridContainer {
   /** A graph describing the subnet dependencies */
   private final SubGridTopologyGraph subGridTopologyGraph;
 
+  private static final Logger logger = LoggerFactory.getLogger(JointGridContainer.class);
+
   public JointGridContainer(
       String gridName,
       RawGridElements rawGrid,
@@ -46,9 +49,10 @@ public JointGridContainer(
    * @param subGridTopologyGraph The graph to check
    */
   private void checkSubGridTopologyGraph(SubGridTopologyGraph subGridTopologyGraph) {
-    if (subGridTopologyGraph.vertexSet().size() == 1)
-      throw new InvalidGridException(
+    if (subGridTopologyGraph.vertexSet().size() == 1) {
+      logger.warn(
           "This joint grid model only contains one single grid. Consider using SubGridContainer.");
+    }
   }
 
   public SubGridTopologyGraph getSubGridTopologyGraph() {

src/test/groovy/edu/ie3/datamodel/models/input/container/JointGridContainerTest.groovy

@@ -0,0 +1,46 @@
+/*
+ * © 2021. TU Dortmund University,
+ * Institute of Energy Systems, Energy Efficiency and Energy Economics,
+ * Research group Distribution grid planning and operation
+ */
+package edu.ie3.datamodel.models.input.container
+
+import edu.ie3.test.common.GridTestData
+import spock.lang.Specification
+
+class JointGridContainerTest extends Specification {
+	private static final GRID_NAME = "single_grid"
+
+	private static final RawGridElements RAW_GRID = new RawGridElements(
+	[GridTestData.nodeA] as Set,
+	[] as Set,
+	[] as Set,
+	[] as Set,
+	[] as Set,
+	[] as Set)
+
+	private static final SystemParticipants SYSTEM_PARTICIPANTS = new SystemParticipants(
+	[] as Set,
+	[] as Set,
+	[] as Set,
+	[] as Set,
+	[] as Set,
+	[] as Set,
+	[] as Set,
+	[] as Set,
+	[] as Set,
+	[] as Set)
+
+	private static final GraphicElements GRAPHIC_ELEMENTS = new GraphicElements(
+	[] as Set,
+	[] as Set)
+
+	def "A single subgrid can be used to build a JointGridContainer"() {
+		when:
+		def jointGridContainer = new JointGridContainer(GRID_NAME, RAW_GRID, SYSTEM_PARTICIPANTS, GRAPHIC_ELEMENTS)
+
+		then:
+		noExceptionThrown()
+		jointGridContainer.subGridTopologyGraph.vertexSet().size() == 1
+	}
+}