Add tests for Dijkstra's algorithm on trivial graphs

tests/dijkstra.rs

@@ -2,6 +2,58 @@ use grapherity::algorithms;
 use grapherity::models::Graph;
 use grapherity::models::Vertex;
 
+#[test]
+fn dijkstra_single_vertex() {
+    let mut graph = Graph::new();
+    let v1 = graph.add_vertex();
+    let (distances, predecessors) = algorithms::dijkstra(&graph, v1);
+    assert_eq!(
+        distances.len(),
+        1,
+        "distances count must equal vertex count"
+    );
+    assert_eq!(
+        predecessors.len(),
+        1,
+        "predecessors count must equal vertex count"
+    );
+    assert_eq!(
+        distances[0],
+        Some(0),
+        "unexpected distance of source vertex"
+    );
+    assert_eq!(
+        predecessors[0], None,
+        "unexpected predecessor of source vertex",
+    );
+}
+
+#[test]
+fn dijkstra_disconnected() {
+    let mut graph = Graph::new();
+    let v1 = graph.add_vertex();
+    graph.add_vertex();
+    let (distances, predecessors) = algorithms::dijkstra(&graph, v1);
+    assert_eq!(
+        distances.len(),
+        2,
+        "distances count must equal vertex count"
+    );
+    assert_eq!(
+        predecessors.len(),
+        2,
+        "predecessors count must equal vertex count"
+    );
+    assert_eq!(
+        distances[1], None,
+        "unexpected distance of disconnected vertex"
+    );
+    assert_eq!(
+        predecessors[0], None,
+        "unexpected predecessor of disconnected vertex",
+    );
+}
+
 #[test]
 fn dijkstra() {
     let (graph, vertices) = make_test_graph();
@@ -33,22 +85,22 @@ fn dijkstra() {
     assert_eq!(
         distances.len(),
         graph.vertex_count(),
-        "distances count from Dijkstra's algorithm must equal vertex count"
+        "distances count must equal vertex count"
     );
     assert_eq!(
         predecessors.len(),
         graph.vertex_count(),
-        "predecessors count from Dijkstra's algorithm must equal vertex count"
+        "predecessors count must equal vertex count"
     );
     for i in 0..graph.vertex_count() {
         assert_eq!(
             distances[i], expected_distances_from_v0[i],
-            "unexpected distance from {:?} to {:?} from Dijkstra's algorithm",
+            "unexpected distance from {:?} to {:?}",
             vertices[0], vertices[i]
         );
         assert!(
             expected_predecessors_from_v0[i].contains(&predecessors[i]),
-            "unexpected predecessor {:?} of {:?} from Dijkstra's algorithm",
+            "unexpected predecessor {:?} of {:?}",
             predecessors[i],
             vertices[i]
         );