feat: add use case diagram examples and update parser tests for error handling

on-behalf-of: @Mermaid-Chart <hello@mermaidchart.com>

packages/examples/src/examples/usecase.ts

@@ -0,0 +1,51 @@
+import type { DiagramMetadata } from '../types.js';
+
+export default {
+  id: 'usecase',
+  name: 'Use Case Diagram',
+  description: 'Visualize system functionality and user interactions',
+  examples: [
+    {
+      title: 'Basic Use Case',
+      isDefault: true,
+      code: `usecase
+actor User
+actor Admin
+User --> (Login)
+User --> (View Profile)
+Admin --> (Manage Users)
+Admin --> (View Reports)`,
+    },
+    {
+      title: 'System Boundary',
+      code: `usecase
+actor Customer
+actor Support
+
+SystemBoundary@{ type: rect } "E-commerce System" {
+  Customer --> (Browse Products)
+  Customer --> (Place Order)
+  Customer --> (Track Order)
+}
+
+SystemBoundary@{ type: package } "Admin Panel" {
+  Support --> (Process Orders)
+  Support --> (Handle Returns)
+}`,
+    },
+    {
+      title: 'Actor Relationships',
+      code: `usecase
+actor Developer1
+actor Developer2
+actor Manager
+
+Developer1 --> (Write Code)
+Developer2 --> (Review Code)
+Manager --> (Approve Release)
+
+Developer1 --> Developer2
+Manager --> Developer1`,
+    },
+  ],
+} satisfies DiagramMetadata;

packages/examples/src/index.ts

@@ -21,6 +21,7 @@ import quadrantChart from './examples/quadrant-chart.js';
 import packetDiagram from './examples/packet.js';
 import blockDiagram from './examples/block.js';
 import treemapDiagram from './examples/treemap.js';
+import usecaseDiagram from './examples/usecase.js';
 
 export const diagramData: DiagramMetadata[] = [
   flowChart,
@@ -45,4 +46,5 @@ export const diagramData: DiagramMetadata[] = [
   packetDiagram,
   blockDiagram,
   treemapDiagram,
+  usecaseDiagram,
 ];

packages/parser/tests/usecase.test.ts

@@ -1489,14 +1489,18 @@ describe('Error Handling', () => {
       const emptyInput = '';
 
       expect(() => parseUsecaseWithAntlr(emptyInput)).toThrow(UsecaseParseError);
-      expect(() => parseUsecaseWithAntlr(emptyInput)).toThrow(/missing 'usecase'/);
+      expect(() => parseUsecaseWithAntlr(emptyInput)).toThrow(
+        /mismatched input '<EOF>' expecting {'usecase', NEWLINE}/
+      );
     });
 
     it('should throw UsecaseParseError for only whitespace input', () => {
       const whitespaceInput = '   \n  \t  \n  ';
 
       expect(() => parseUsecaseWithAntlr(whitespaceInput)).toThrow(UsecaseParseError);
-      expect(() => parseUsecaseWithAntlr(whitespaceInput)).toThrow(/missing 'usecase'/);
+      expect(() => parseUsecaseWithAntlr(whitespaceInput)).toThrow(
+        /extraneous input '<EOF>' expecting {'usecase', NEWLINE}/
+      );
     });
 
     it('should throw UsecaseParseError for missing usecase keyword', () => {
@@ -1506,7 +1510,9 @@ describe('Error Handling', () => {
       `;
 
       expect(() => parseUsecaseWithAntlr(missingKeyword)).toThrow(UsecaseParseError);
-      expect(() => parseUsecaseWithAntlr(missingKeyword)).toThrow(/missing 'usecase'/);
+      expect(() => parseUsecaseWithAntlr(missingKeyword)).toThrow(
+        /extraneous input 'actor' expecting {'usecase', NEWLINE}/
+      );
     });
   });