diff --git a/jest.config.ts b/jest.config.ts
index 73738651..3a9741cf 100644
--- a/jest.config.ts
+++ b/jest.config.ts
@@ -4,4 +4,13 @@ export default {
   transform: {
     '^.+\\.(ts|tsx)$': 'ts-jest',
   },
+  moduleNameMapper: {
+    '^assets/(.*)$': '<rootDir>/src/assets/$1',
+    '^components/(.*)$': '<rootDir>/src/components/$1',
+    '^lib/(.*)$': '<rootDir>/src/lib/$1',
+    '^pages/(.*)$': '<rootDir>/src/pages/$1',
+    '^queries/(.*)$': '<rootDir>/src/queries/$1',
+    '^store/(.*)$': '<rootDir>/src/store/$1',
+    '^styles/(.*)$': '<rootDir>/src/styles/$1',
+  },
 };
diff --git a/src/lib/__tests__/charts.test.ts b/src/lib/__tests__/charts.test.ts
new file mode 100644
index 00000000..cd9e8651
--- /dev/null
+++ b/src/lib/__tests__/charts.test.ts
@@ -0,0 +1,80 @@
+import { renderNumberLabels, renderDateLabels } from 'lib/charts';
+import { formatDate } from 'lib/date';
+
+// test for renderNumberLabels
+
+describe('renderNumberLabels', () => {
+  test.each([
+    ['1000000', '1.0m'],
+    ['2500000', '2.5m'],
+  ])("formats numbers ≥ 1 million as 'Xm' (%s → %s)", (input, expected) => {
+    expect(renderNumberLabels(input)).toBe(expected);
+  });
+
+  test.each([['150000', '150k']])("formats numbers ≥ 100K as 'Xk' (%s → %s)", (input, expected) => {
+    expect(renderNumberLabels(input)).toBe(expected);
+  });
+
+  test.each([['12500', '12.5k']])(
+    "formats numbers ≥ 10K as 'X.Xk' (%s → %s)",
+    (input, expected) => {
+      expect(renderNumberLabels(input)).toBe(expected);
+    },
+  );
+
+  test.each([['1500', '1.50k']])("formats numbers ≥ 1K as 'X.XXk' (%s → %s)", (input, expected) => {
+    expect(renderNumberLabels(input)).toBe(expected);
+  });
+
+  test.each([['999', '999']])(
+    'calls formatNumber for values < 1000 (%s → %s)',
+    (input, expected) => {
+      expect(renderNumberLabels(input)).toBe(expected);
+    },
+  );
+
+  test.each([
+    ['0', '0'],
+    ['-5000', '-5000'],
+  ])('handles edge cases correctly (%s → %s)', (input, expected) => {
+    expect(renderNumberLabels(input)).toBe(expected);
+  });
+});
+
+describe('renderDateLabels', () => {
+  const mockValues = [{ value: '2024-03-23T10:00:00Z' }, { value: '2024-03-24T15:30:00Z' }];
+
+  beforeEach(() => {
+    jest.spyOn(require('lib/date'), 'formatDate');
+  });
+
+  afterEach(() => {
+    jest.restoreAllMocks(); // Reset spy to prevent interference
+  });
+
+  test.each([
+    ['minute', 'h:mm', 'en-US'],
+    ['hour', 'p', 'en-US'],
+    ['day', 'MMM d', 'en-US'],
+    ['month', 'MMM', 'en-US'],
+    ['year', 'yyyy', 'en-US'],
+  ])('formats date correctly for unit: %s', (unit, expectedFormat, locale) => {
+    const formatLabel = renderDateLabels(unit, locale);
+    const formatted = formatLabel('label', 0, mockValues);
+
+    expect(formatDate).toHaveBeenCalledWith(new Date(mockValues[0].value), expectedFormat, locale);
+    expect(formatted).toBe(formatDate(new Date(mockValues[0].value), expectedFormat, locale));
+  });
+
+  test('returns label for unknown unit', () => {
+    const formatLabel = renderDateLabels('unknown', 'en-US');
+    expect(formatLabel('original-label', 0, mockValues)).toBe('original-label');
+  });
+
+  test('throws error for invalid date input', () => {
+    const invalidValues = [{ value: 'invalid-date' }];
+    const formatLabel = renderDateLabels('day', 'en-US');
+
+    expect(() => formatLabel('label', 0, invalidValues)).toThrow();
+  });
+});
diff --git a/src/lib/charts.ts b/src/lib/charts.ts
index d6917c83..957d4962 100644
--- a/src/lib/charts.ts
+++ b/src/lib/charts.ts
@@ -19,7 +19,7 @@ export function renderDateLabels(unit: string, locale: string) {
       case 'month':
         return formatDate(d, 'MMM', locale);
       case 'year':
-        return formatDate(d, 'YYY', locale);
+        return formatDate(d, 'yyyy', locale);
       default:
         return label;
     }