Ensure valid values for transferCount

Author: leonardehrenfried

application/src/test/java/org/opentripplanner/gtfs/mapping/FareTransferRuleMapperTest.java

@@ -109,6 +109,17 @@ void defaultTransferCount() {
     assertTrue(transferRule.unlimitedTransfers());
   }
 
+  @Test
+  void explicitUnlimitedTransfer() {
+    var rule = new FareTransferRule();
+    rule.setFromLegGroupId(groupId1);
+    rule.setToLegGroupId(groupId2);
+    rule.setTransferCount(-1);
+
+    var transferRule = map(fareProduct(), rule);
+    assertTrue(transferRule.unlimitedTransfers());
+  }
+
   @Test
   void transferCount() {
     var rule = new FareTransferRule();