add diagram renderer mocks

__mocks__/c4Renderer.js

@@ -0,0 +1,21 @@
+/**
+ * Mocked C4Context diagram renderer
+ */
+
+import { vi } from 'vitest';
+
+export const drawPersonOrSystemArray = vi.fn();
+export const drawBoundary = vi.fn();
+
+export const setConf = vi.fn();
+
+export const draw = vi.fn().mockImplementation(() => {
+  return '';
+});
+
+export default {
+  drawPersonOrSystemArray,
+  drawBoundary,
+  setConf,
+  draw,
+};