Add comprehensive keyboard navigation tests for dropdown components

- Add tests for ArrowUp/ArrowDown navigation in month dropdown
- Add tests for Escape key handling in month dropdown
- Add tests for month wrapping (first->last, last->first)
- Add tests for Enter/Escape/Arrow keys in year dropdown
- Improves test coverage to 100% line coverage for both components
- Resolves Codecov coverage gaps in dropdown keyboard accessibility

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: martijnrusschen

src/test/month_dropdown_test.test.tsx

@@ -214,6 +214,83 @@ describe("MonthDropdown", () => {
       fireEvent.keyDown(document.activeElement!, { key: "Enter" });
       expect(handleChangeResult).toEqual(4);
     });
+
+    it("handles ArrowUp key navigation correctly", () => {
+      const monthReadView = safeQuerySelector(
+        monthDropdown,
+        ".react-datepicker__month-read-view",
+      );
+      fireEvent.click(monthReadView);
+
+      const monthOptions = safeQuerySelectorAll(
+        monthDropdown,
+        ".react-datepicker__month-option",
+      );
+
+      const monthOption = monthOptions[5]!;
+      fireEvent.keyDown(monthOption, { key: "ArrowUp" });
+
+      const prevMonthOption = monthOptions[4];
+      expect(document.activeElement).toEqual(prevMonthOption);
+    });
+
+    it("handles Escape key to cancel dropdown", () => {
+      const monthReadView = safeQuerySelector(
+        monthDropdown,
+        ".react-datepicker__month-read-view",
+      );
+      fireEvent.click(monthReadView);
+
+      const monthOptions = safeQuerySelectorAll(
+        monthDropdown,
+        ".react-datepicker__month-option",
+      );
+
+      const monthOption = monthOptions[5]!;
+      fireEvent.keyDown(monthOption, { key: "Escape" });
+
+      expect(
+        monthDropdown?.querySelectorAll(".react-datepicker__month-dropdown"),
+      ).toHaveLength(0);
+    });
+
+    it("wraps around when using ArrowUp on first month", () => {
+      const monthReadView = safeQuerySelector(
+        monthDropdown,
+        ".react-datepicker__month-read-view",
+      );
+      fireEvent.click(monthReadView);
+
+      const monthOptions = safeQuerySelectorAll(
+        monthDropdown,
+        ".react-datepicker__month-option",
+      );
+
+      const firstMonthOption = monthOptions[0]!;
+      fireEvent.keyDown(firstMonthOption, { key: "ArrowUp" });
+
+      const lastMonthOption = monthOptions[11];
+      expect(document.activeElement).toEqual(lastMonthOption);
+    });
+
+    it("wraps around when using ArrowDown on last month", () => {
+      const monthReadView = safeQuerySelector(
+        monthDropdown,
+        ".react-datepicker__month-read-view",
+      );
+      fireEvent.click(monthReadView);
+
+      const monthOptions = safeQuerySelectorAll(
+        monthDropdown,
+        ".react-datepicker__month-option",
+      );
+
+      const lastMonthOption = monthOptions[11]!;
+      fireEvent.keyDown(lastMonthOption, { key: "ArrowDown" });
+
+      const firstMonthOption = monthOptions[0];
+      expect(document.activeElement).toEqual(firstMonthOption);
+    });
   });
 
   describe("select mode", () => {

src/test/year_dropdown_options_test.test.tsx

@@ -146,6 +146,76 @@ describe("YearDropdownOptions", () => {
     expect(onCancelSpy).toHaveBeenCalledTimes(2);
   });
 
+  it("handles Enter key to select year", () => {
+    const yearOptions = safeQuerySelectorAll(
+      yearDropdown,
+      ".react-datepicker__year-option",
+    );
+    const year2014Option = yearOptions.find((node) =>
+      node.textContent?.includes("2014"),
+    );
+
+    if (!year2014Option) {
+      throw new Error("Year 2014 not found!");
+    }
+
+    fireEvent.keyDown(year2014Option, { key: "Enter" });
+    expect(handleChangeResult).toBe(2014);
+  });
+
+  it("handles Escape key to cancel dropdown", () => {
+    const yearOptions = safeQuerySelectorAll(
+      yearDropdown,
+      ".react-datepicker__year-option",
+    );
+    const year2014Option = yearOptions.find((node) =>
+      node.textContent?.includes("2014"),
+    );
+
+    if (!year2014Option) {
+      throw new Error("Year 2014 not found!");
+    }
+
+    fireEvent.keyDown(year2014Option, { key: "Escape" });
+    expect(onCancelSpy).toHaveBeenCalled();
+  });
+
+  it("handles ArrowUp key navigation", () => {
+    const yearOptions = safeQuerySelectorAll(
+      yearDropdown,
+      ".react-datepicker__year-option",
+    );
+    const year2015Option = yearOptions.find((node) =>
+      node.textContent?.includes("✓2015"),
+    );
+
+    if (!year2015Option) {
+      throw new Error("Year 2015 not found!");
+    }
+
+    fireEvent.keyDown(year2015Option, { key: "ArrowUp" });
+    // ArrowUp should focus year 2016 (year + 1 in the code)
+    expect(document.activeElement?.textContent).toContain("2016");
+  });
+
+  it("handles ArrowDown key navigation", () => {
+    const yearOptions = safeQuerySelectorAll(
+      yearDropdown,
+      ".react-datepicker__year-option",
+    );
+    const year2015Option = yearOptions.find((node) =>
+      node.textContent?.includes("✓2015"),
+    );
+
+    if (!year2015Option) {
+      throw new Error("Year 2015 not found!");
+    }
+
+    fireEvent.keyDown(year2015Option, { key: "ArrowDown" });
+    // ArrowDown should focus year 2014 (year - 1 in the code)
+    expect(document.activeElement?.textContent).toContain("2014");
+  });
+
   describe("selected", () => {
     const className = "react-datepicker__year-option--selected_year";
     let yearOptions: HTMLElement[];