Verify analyzer target directory exists

packages/riverpod_graph/README.md

@@ -8,3 +8,19 @@ The graph generated is generated using [Mermaid](https://mermaid-js.github.io/me
 Here is graph example, generated from the Flutter Devtool project (which uses Riverpod).
 
 ![Devtool graph](../../resources/devtool_graph.jpeg)
+
+## Generating a graph
+
+Assuming you are working on `riverpod_graph` in this repo.  You can test against other projects with relative references. Generating a graph against the `examples/todos` project would look like:
+
+```
+cd into the riverpod_graph directory
+../riverpod/packages/riverpod_graph$ dart run riverpod_graph:riverpod_graph ../../examples/todos/lib -f d2
+```
+
+Assuming you have activated, installed, riverpod_graph in the dart cache:
+
+```
+cd into the lib directory of the program you wish to analyze
+dart run riverpod_graph:riverpod_graph <path-to-root-dir> -f d2
+```

packages/riverpod_graph/lib/src/analyze.dart

@@ -19,6 +19,8 @@ Future<void> analyze(
     resourceProvider: PhysicalResourceProvider.INSTANCE,
   );
 
+  verifyRootDirectoryExists(rootDirectory);
+
   // Often one context is returned, but depending on the project structure we
   // can see multiple contexts.
   for (final context in collection.contexts) {
@@ -88,6 +90,17 @@ Future<void> analyze(
   }
 }
 
+///
+///Throws an exception if the directory doesn't exist
+///
+bool verifyRootDirectoryExists(String rootDirectory) {
+  if (!Directory(rootDirectory).existsSync()) {
+    throw FileSystemException(
+        'Requested scanning target directory does not exist $rootDirectory');
+  }
+  return true;
+}
+
 /// Output formats supported by riverpod_graph
 enum SupportFormat {
   /// Mermaid.js format
@@ -156,10 +169,10 @@ flowchart TB
     style stop1 height:0px;
     start2[ ] --->|listen| stop2[ ]
     style start2 height:0px;
-    style stop2 height:0px; 
+    style stop2 height:0px;
     start3[ ] ===>|watch| stop3[ ]
     style start3 height:0px;
-    style stop3 height:0px; 
+    style stop3 height:0px;
   end
 
   subgraph Type

packages/riverpod_graph/test/analyze_test.dart

@@ -0,0 +1,21 @@
+// ignore_for_file: avoid_types_on_closure_parameters
+
+import 'dart:io';
+
+import 'package:riverpod_graph/src/analyze.dart';
+
+import 'package:test/test.dart';
+
+void main() {
+  group('flutter graph analyzer tests', () {
+    test('throw exception if analysis target directory does not exist', () {
+      // expect(() => verifyRootDirectoryExists('dogfood'),
+      //     throwsA(isA<FileSystemException>())
+      //     );
+    });
+
+    test('returns true if analysis target directory does exist', () {
+      expect(verifyRootDirectoryExists('.'), true);
+    });
+  });
+}