test: add test case for constructor options with explicit undefined…

… values

tests/signature_pad.test.ts

@@ -1,4 +1,5 @@
 import SignaturePad from '../src/signature_pad';
+import type { Options } from '../src/signature_pad';
 import { face } from './fixtures/face';
 import { square } from './fixtures/square';
 import './utils/pointer-event-polyfill';
@@ -37,6 +38,51 @@ describe('#constructor', () => {
 
     expect(pad.minDistance).toBe(0);
   });
+
+  it("uses fallback values for options with explicit 'undefined'", () => {
+    const opts: Options = {
+      dotSize: undefined,
+      minWidth: undefined,
+      maxWidth: undefined,
+      penColor: undefined,
+      velocityFilterWeight: undefined,
+      compositeOperation: undefined,
+      minDistance: undefined,
+      backgroundColor: undefined,
+      throttle: undefined,
+      canvasContextOptions: undefined,
+    };
+
+    const exp: Options = {
+      dotSize: 0,
+      minWidth: 0.5,
+      maxWidth: 2.5,
+      penColor: 'black',
+      velocityFilterWeight: 0.7,
+      compositeOperation: 'source-over',
+      minDistance: 5,
+      backgroundColor: 'rgba(0,0,0,0)',
+      throttle: 16,
+      canvasContextOptions: {},
+    };
+
+    const pad = new SignaturePad(canvas, opts);
+
+    const actual = {
+      dotSize: pad.dotSize,
+      minWidth: pad.minWidth,
+      maxWidth: pad.maxWidth,
+      penColor: pad.penColor,
+      velocityFilterWeight: pad.velocityFilterWeight,
+      compositeOperation: pad.compositeOperation,
+      minDistance: pad.minDistance,
+      backgroundColor: pad.backgroundColor,
+      throttle: pad.throttle,
+      canvasContextOptions: pad.canvasContextOptions,
+    };
+
+    expect(actual).toStrictEqual(exp);
+  });
 });
 
 describe('#clear', () => {