move client from separate repo

client/tests/mocks/source.mock.ts

@@ -0,0 +1,18 @@
+import { Observable } from 'rxjs'
+import { UpdateReal } from '../../lib/sequence-store'
+import { Source } from '../../lib/source/source'
+
+export class MockSource<T> implements Source<T> {
+
+  constructor (
+    private readonly mockData: Observable<UpdateReal<T>>,
+  ) { }
+
+  watch$ (): Observable<UpdateReal<T>> {
+    return this.mockData
+  }
+
+  start (): void {  }
+
+  stop (): void {  }
+}