Move common test helpers to fixtures module

tests/dfs.rs

@@ -2,6 +2,7 @@ use std::fmt::Debug;
 
 use grapherity::algorithms;
 use grapherity::maps::ElementMap;
+use grapherity::testing::fixtures;
 use grapherity::testing::fixtures::MakeTestGraph;
 use grapherity::traits::GraphTopology;
 
@@ -257,12 +258,7 @@ where
     let (graph, vertices, e) = G::single_edge();
     let path = algorithms::dfs_find_path(&graph, vertices[0], vertices[1])
         .expect("path should exist between adjacent vertices");
-    assert_eq!(
-        path.len(),
-        1,
-        "unexpected path length between adjacent vertices"
-    );
-    assert_eq!(path[0], e, "path should use the connecting edge");
+    assert_eq!(path, [e], "path should contain only the connecting edge");
 }
 
 fn dfs_find_path<G: MakeTestGraph>()
@@ -271,11 +267,8 @@ where
     G::Edge: Debug,
 {
     let (graph, vertices, _, _) = G::standard();
-    let path = algorithms::dfs_find_path(&graph, vertices[0], vertices[9]).expect(&format!(
-        "path should exist between connected vertices {:?} and {:?}",
-        vertices[0], vertices[9]
-    ));
-    assert_valid_path(&graph, &path, vertices[0], vertices[9]);
+    let path = algorithms::dfs_find_path(&graph, vertices[0], vertices[9]);
+    fixtures::assert_valid_path(&graph, path, vertices[0], &[vertices[9]]);
 }
 
 fn dfs_find_path_where_source_matches<G: MakeTestGraph>()
@@ -320,13 +313,8 @@ where
     G::Edge: Debug,
 {
     let (graph, vertices, _, _) = G::standard();
-    let path = algorithms::dfs_find_path_where(&graph, vertices[0], |v| v == vertices[9]).expect(
-        &format!(
-            "path should exist between connected vertices {:?} and {:?}",
-            vertices[0], vertices[9]
-        ),
-    );
-    assert_valid_path(&graph, &path, vertices[0], vertices[9]);
+    let path = algorithms::dfs_find_path_where(&graph, vertices[0], |v| v == vertices[9]);
+    _ = fixtures::assert_valid_path(&graph, path, vertices[0], &[vertices[9]]);
 }
 
 fn assert_dfs_visited<G: GraphTopology>(
@@ -369,30 +357,3 @@ fn assert_dfs_predecessors<G: GraphTopology>(
         );
     }
 }
-
-fn assert_valid_path<G: GraphTopology>(
-    graph: &G,
-    path: &[G::Edge],
-    source: G::Vertex,
-    target: G::Vertex,
-) where
-    G::Vertex: Debug,
-    G::Edge: Debug,
-{
-    assert!(!path.is_empty(), "path should be non-empty");
-    // Walks the path: tracks current vertex, confirm each edge is incident to it.
-    let mut current = source;
-    for (i, &e) in path.iter().enumerate() {
-        let (v1, v2) = graph.incident_vertices(e);
-        assert_ne!(v1, v2, "path should not contain loop edge {e:?}");
-        assert!(
-            v1 == current || v2 == current,
-            "path edge {e:?} (idx {i}, {v1:?} to {v2:?}) not incident to vertex {current:?}"
-        );
-        current = if v1 == current { v2 } else { v1 };
-    }
-    assert_eq!(
-        current, target,
-        "path should end at target {target:?}, but ended at {current:?}"
-    );
-}