Adhere to iterator contract

Author: leonardehrenfried

street/src/main/java/org/opentripplanner/street/search/state/BackEdgeIterator.java

@@ -1,6 +1,7 @@
 package org.opentripplanner.street.search.state;
 
 import java.util.Iterator;
+import java.util.NoSuchElementException;
 import org.opentripplanner.street.model.edge.Edge;
 
 /**
@@ -21,6 +22,9 @@ public boolean hasNext() {
 
   @Override
   public Edge next() {
+    if(!hasNext()){
+      throw new NoSuchElementException("No more back edges available");
+    }
     var ret = current;
     current = current.getBackState();
     return ret.getBackEdge();

street/src/test/java/org/opentripplanner/street/search/state/BackEdgeIteratorTest.java

@@ -1,6 +1,8 @@
 package org.opentripplanner.street.search.state;
 
 import static com.google.common.truth.Truth.assertThat;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.params.provider.Arguments.of;
 import static org.opentripplanner.street.search.state.TestStateBuilder.ofBikeRental;
 import static org.opentripplanner.street.search.state.TestStateBuilder.ofCycling;
@@ -9,6 +11,8 @@
 
 import com.google.common.collect.ImmutableList;
 import java.util.List;
+import java.util.NoSuchElementException;
+import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.MethodSource;
@@ -32,5 +36,18 @@ void countEdges(State state, int expectedSize) {
     var edges = ImmutableList.copyOf(state.listBackEdges());
     assertThat(edges).hasSize(expectedSize);
     assertThat(edges).doesNotContain(null);
+
+  }
+
+  @Test
+  void exception(){
+    var state = TestStateBuilder.ofWalking().streetEdge().build();
+    var iterator = state.listBackEdges().iterator();
+    var edges = ImmutableList.copyOf(iterator);
+    assertThat(edges).hasSize(1);
+
+    assertFalse(iterator.hasNext());
+
+    assertThrows(NoSuchElementException.class, iterator::next);
   }
 }