diff --git a/src/FlagOverrides.test.tsx b/src/FlagOverrides.test.tsx
new file mode 100644
index 0000000..197b4ec
--- /dev/null
+++ b/src/FlagOverrides.test.tsx
@@ -0,0 +1,105 @@
+import { cleanup, render, screen } from "@testing-library/react";
+import React from "react";
+import { useFeatureFlag } from "./ConfigCatHooks";
+import ConfigCatProvider from "./ConfigCatProvider";
+import type { IQueryStringProvider, IReactAutoPollOptions } from ".";
+import { OverrideBehaviour, createFlagOverridesFromQueryParams } from ".";
+
+const sdkKey = "PKDVCLf-Hq-h-kCzMp-L7Q/psuH7BGHoUmdONrzzUOY7A";
+
+afterEach(cleanup);
+
+describe("Flag Overrides", () => {
+  it("Query string override should work - changes not watched", async () => {
+    const TestComponent = () => {
+      const { value: featureFlag } = useFeatureFlag("stringDefaultCat", "NOT_CAT");
+      return (< div>Feature flag value: {featureFlag}</div>);
+    };
+
+    const queryStringProvider: IQueryStringProvider & { currentValue?: string } = {
+      currentValue: "?cc-stringDefaultCat=OVERRIDE_CAT&stringDefaultCat=NON_OVERRIDE_CAT"
+    };
+
+    const options: IReactAutoPollOptions = {
+      flagOverrides: createFlagOverridesFromQueryParams(OverrideBehaviour.LocalOverRemote, false, void 0, queryStringProvider)
+    };
+
+    const ui = <ConfigCatProvider sdkKey={sdkKey} options={options}><TestComponent /></ConfigCatProvider>;
+
+    await render(ui);
+    await screen.findByText("Feature flag value: OVERRIDE_CAT", void 0, { timeout: 2000 });
+
+    cleanup();
+    queryStringProvider.currentValue = "?cc-stringDefaultCat=CHANGED_OVERRIDE_CAT";
+
+    await render(ui);
+    await screen.findByText("Feature flag value: OVERRIDE_CAT", void 0, { timeout: 2000 });
+  });
+
+  it("Query string override should work - changes watched", async () => {
+    const TestComponent = () => {
+      const { value: featureFlag } = useFeatureFlag("stringDefaultCat", "NOT_CAT");
+      return (< div>Feature flag value: {featureFlag}</div>);
+    };
+
+    const queryStringProvider: IQueryStringProvider & { currentValue?: string } = {
+      currentValue: "?cc-stringDefaultCat=OVERRIDE_CAT"
+    };
+
+    const options: IReactAutoPollOptions = {
+      flagOverrides: createFlagOverridesFromQueryParams(OverrideBehaviour.LocalOverRemote, true, void 0, queryStringProvider)
+    };
+
+    const ui = <ConfigCatProvider sdkKey={sdkKey} options={options}><TestComponent /></ConfigCatProvider>;
+
+    await render(ui);
+    await screen.findByText("Feature flag value: OVERRIDE_CAT", void 0, { timeout: 2000 });
+
+    cleanup();
+    queryStringProvider.currentValue = "?cc-stringDefaultCat=CHANGED_OVERRIDE_CAT";
+
+    await render(ui);
+    await screen.findByText("Feature flag value: CHANGED_OVERRIDE_CAT", void 0, { timeout: 2000 });
+  });
+
+  it("Query string override should work - respects custom prefix", async () => {
+    const TestComponent = () => {
+      const { value: featureFlag } = useFeatureFlag("stringDefaultCat", "NOT_CAT");
+      return (< div>Feature flag value: {featureFlag}</div>);
+    };
+
+    const queryStringProvider: IQueryStringProvider & { currentValue?: string } = {
+      currentValue: "?stringDefaultCat=OVERRIDE_CAT&cc-stringDefaultCat=NON_OVERRIDE_CAT"
+    };
+
+    const options: IReactAutoPollOptions = {
+      flagOverrides: createFlagOverridesFromQueryParams(OverrideBehaviour.LocalOverRemote, void 0, "", queryStringProvider)
+    };
+
+    const ui = <ConfigCatProvider sdkKey={sdkKey} options={options}><TestComponent /></ConfigCatProvider>;
+
+    await render(ui);
+    await screen.findByText("Feature flag value: OVERRIDE_CAT", void 0, { timeout: 2000 });
+  });
+
+  it("Query string override should work - handles query string edge cases", async () => {
+    const TestComponent = () => {
+      const { value: featureFlag } = useFeatureFlag("stringDefaultCat", "NOT_CAT");
+      return (< div>Feature flag value: {featureFlag}</div>);
+    };
+
+    const queryStringProvider: IQueryStringProvider & { currentValue?: string } = {
+      currentValue: "?&some&=garbage&&cc-stringDefaultCat=OVERRIDE_CAT&=cc-stringDefaultCat&cc-stringDefaultCat"
+    };
+
+    const options: IReactAutoPollOptions = {
+      flagOverrides: createFlagOverridesFromQueryParams(OverrideBehaviour.LocalOverRemote, void 0, void 0, queryStringProvider)
+    };
+
+    const ui = <ConfigCatProvider sdkKey={sdkKey} options={options}><TestComponent /></ConfigCatProvider>;
+
+    await render(ui);
+    await screen.findByText("Feature flag value:", void 0, { timeout: 2000 });
+    await expect(() => screen.findByText("Feature flag value: OVERRIDE_CAT", void 0, { timeout: 2000 })).rejects.toThrow();
+  });
+});