Add unit test cases for useStylesInternal hook (#250)

__tests__/hooks/internal/useStylesInternal.test.ts

@@ -0,0 +1,60 @@
+import { renderHook, act } from "@testing-library/react";
+import { expect } from "@jest/globals";
+
+import { useStylesInternal } from "../../../src/hooks/internal/useStylesInternal";
+import { useStylesContext } from "../../../src/context/StylesContext";
+import { parseConfig } from "../../../src/utils/configParser";
+
+// Mock the necessary context and service
+jest.mock("../../../src/context/StylesContext");
+jest.mock("../../../src/utils/configParser", () => ({
+    deepClone: jest.fn(),
+    getCombinedConfig: jest.fn(),
+}));
+
+/**
+ * Test for useStylesInternal hook.
+ */
+describe("useStylesInternal Hook", () => {
+    const setStylesMock = jest.fn();
+    const stylesMock = {
+        bodyStyle: {}
+    }
+
+    beforeEach(() => {
+        jest.clearAllMocks();
+        (useStylesContext as jest.Mock).mockReturnValue({ styles: stylesMock, setStyles: setStylesMock});
+    })
+
+    // Test to ensure initial values (styels and setStyles) are returned correctly from the hook
+    it("should return initial values from context", () => {
+        const { result } = renderHook(() => useStylesInternal());
+
+        expect(result.current.styles).toEqual(stylesMock);
+        expect(result.current.replaceStyles).toEqual(expect.any(Function));
+        expect(result.current.updateStyles).toEqual(expect.any(Function));
+    });
+
+    it("should call setStyles from context, when styles are updated", () => {
+        const { result } = renderHook(() => useStylesInternal());
+        const styles = { tooltipStyle: {} };
+
+        act(() => {
+			result.current.updateStyles(styles);
+		});
+        // Argument passed to setStyles is not checked, because it is transformed with 
+        // deepClone() and getCombinedConfig()
+        expect(setStylesMock).toHaveBeenCalled();
+    });
+
+    it("should call setStyles from context with correct value, when styles are replaced", () => {
+        const { result } = renderHook(() => useStylesInternal());
+        const styles = { notificationBadgeStyle: {} };
+
+        act(() => {
+			result.current.replaceStyles(styles);
+		});
+
+        expect(setStylesMock).toHaveBeenCalledWith(styles);
+    });
+});