Add error handling for shortest path

Author: curran

index.js

@@ -213,6 +213,12 @@ module.exports = function Graph(serialized){
       nodes().forEach(function (node){
         d[node] = Infinity;
       });
+      if (d[source] !== Infinity) {
+        throw new Error("Source node is not in the graph");
+      }
+      if (d[destination] !== Infinity) {
+        throw new Error("Destination node is not in the graph");
+      }
       d[source] = 0;
     }
 
@@ -238,6 +244,9 @@ module.exports = function Graph(serialized){
           minNode = node;
         }
       });
+      if (minNode === undefined) {
+        throw new Error("No path exists.");
+      }
       delete q[minNode];
       return minNode;
     }

test.js

@@ -362,6 +362,22 @@ describe("Graph", function() {
       assert.deepEqual(graph.shortestPath("s", "x"), ["s", "y", "t", "x"]);
     });
 
+    it("Should throw error if source node not in graph.", function (){
+      var graph = Graph().addEdge("b", "c");
+      assert.throws(() => graph.shortestPath("a", "c"), /Source node/);
+    });
+
+    it("Should throw error if dest node not in graph.", function (){
+      var graph = Graph().addEdge("b", "c");
+      assert.throws(() => graph.shortestPath("b", "g"), /Destination node/);
+    });
+
+    it("Should throw error if no path exists.", function (){
+      var graph = Graph()
+        .addEdge("a", "b")
+        .addEdge("d", "e");
+      assert.throws(() => graph.shortestPath("a", "e"), /No path/);
+    });
   });
 });