refactor: CheckFreshness and DiffDiagram take &str instead of &Path

crates/application/tests/diff_diagram_tests.rs

@@ -0,0 +1,44 @@
+mod fakes;
+
+use archlens_domain::{CodeGraph, NormalizedGraph, ports::DiagramRenderer};
+use archlens_application::use_cases::diff_diagram::DiffDiagram;
+use fakes::FakeDiagramRenderer;
+
+fn empty_graph() -> NormalizedGraph {
+    NormalizedGraph::from_project(CodeGraph::new())
+}
+
+#[test]
+fn no_diff_when_content_matches() {
+    let graph = empty_graph();
+    let renderer = FakeDiagramRenderer::new();
+    let rendered = renderer.render(graph.as_graph()).unwrap();
+    let existing = rendered.files().first().unwrap().content().to_string();
+
+    let result = DiffDiagram {
+        graph: &graph,
+        renderer: &renderer,
+        existing_content: &existing,
+    }
+    .execute()
+    .unwrap();
+
+    assert!(result.is_empty());
+}
+
+#[test]
+fn detects_added_lines() {
+    let graph = empty_graph();
+    let renderer = FakeDiagramRenderer::new();
+
+    let result = DiffDiagram {
+        graph: &graph,
+        renderer: &renderer,
+        existing_content: "old line that will be removed",
+    }
+    .execute()
+    .unwrap();
+
+    assert!(!result.added.is_empty());
+    assert!(!result.removed.is_empty());
+}