Move stubs from ./stubs to ./shared/Stubs

Gathers all shared test code in single place.

tests/unit/shared/Stubs/EnvironmentStub.ts

@@ -0,0 +1,13 @@
+import { IEnvironment } from '@/application/Environment/IEnvironment';
+import { OperatingSystem } from '@/domain/OperatingSystem';
+
+export class EnvironmentStub implements IEnvironment {
+  public isDesktop = true;
+
+  public os = OperatingSystem.Windows;
+
+  public withOs(os: OperatingSystem): EnvironmentStub {
+    this.os = os;
+    return this;
+  }
+}