fix: Make IDP routes independent of handlers

test/unit/identity/interaction/routing/RelativePathInteractionRoute.test.ts

@@ -0,0 +1,24 @@
+import type { InteractionRoute } from '../../../../../src/identity/interaction/routing/InteractionRoute';
+import {
+  RelativePathInteractionRoute,
+} from '../../../../../src/identity/interaction/routing/RelativePathInteractionRoute';
+
+describe('A RelativePathInteractionRoute', (): void => {
+  const relativePath = '/relative/';
+  let route: jest.Mocked<InteractionRoute>;
+  let relativeRoute: RelativePathInteractionRoute;
+
+  beforeEach(async(): Promise<void> => {
+    route = {
+      getPath: jest.fn().mockReturnValue('http://example.com/'),
+    };
+  });
+
+  it('returns the joined path.', async(): Promise<void> => {
+    relativeRoute = new RelativePathInteractionRoute(route, relativePath);
+    expect(relativeRoute.getPath()).toBe('http://example.com/relative/');
+
+    relativeRoute = new RelativePathInteractionRoute('http://example.com/test/', relativePath);
+    expect(relativeRoute.getPath()).toBe('http://example.com/test/relative/');
+  });
+});