feat: add volume conversion litres to gallons and vice versa

Conversions/VolumeConversion.js

@@ -0,0 +1,33 @@
+/**
+ * @function litresToGallons
+ * @description Converts volume from litres to US gallons.
+ * @param {number} litres - Volume in litres
+ * @returns {number} - Volume in US gallons
+ * @see https://en.wikipedia.org/wiki/Gallon
+ * @example litresToGallons(1) => 0.264172
+ * @example litresToGallons(10) => 2.64172
+ */
+const litresToGallons = (litres) => {
+  if (typeof litres !== 'number' || isNaN(litres)) {
+    throw new TypeError('Input must be a number')
+  }
+  return litres * 0.264172
+}
+
+/**
+ * @function gallonsToLitres
+ * @description Converts volume from US gallons to litres.
+ * @param {number} gallons - Volume in US gallons
+ * @returns {number} - Volume in litres
+ * @see https://en.wikipedia.org/wiki/Litre
+ * @example gallonsToLitres(1) => 3.78541
+ * @example gallonsToLitres(10) => 37.8541
+ */
+const gallonsToLitres = (gallons) => {
+  if (typeof gallons !== 'number' || isNaN(gallons)) {
+    throw new TypeError('Input must be a number')
+  }
+  return gallons * 3.78541
+}
+
+export { litresToGallons, gallonsToLitres }

Conversions/test/VolumeConversion.test.js

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+import { litresToGallons, gallonsToLitres } from '../VolumeConversion.js'
+
+describe('litresToGallons', () => {
+  test('litresToGallons(0) returns 0', () => {
+    expect(litresToGallons(0)).toBe(0)
+  })
+
+  test('litresToGallons(1) returns 0.264172', () => {
+    expect(litresToGallons(1)).toBeCloseTo(0.264172)
+  })
+
+  test('litresToGallons(10) returns 2.64172', () => {
+    expect(litresToGallons(10)).toBeCloseTo(2.64172)
+  })
+
+  test('litresToGallons(100) returns 26.4172', () => {
+    expect(litresToGallons(100)).toBeCloseTo(26.4172)
+  })
+
+  test('throws TypeError for non-number input', () => {
+    expect(() => litresToGallons('10')).toThrow(TypeError)
+  })
+
+  test('throws TypeError for NaN', () => {
+    expect(() => litresToGallons(NaN)).toThrow(TypeError)
+  })
+})
+
+describe('gallonsToLitres', () => {
+  test('gallonsToLitres(0) returns 0', () => {
+    expect(gallonsToLitres(0)).toBe(0)
+  })
+
+  test('gallonsToLitres(1) returns 3.78541', () => {
+    expect(gallonsToLitres(1)).toBeCloseTo(3.78541)
+  })
+
+  test('gallonsToLitres(10) returns 37.8541', () => {
+    expect(gallonsToLitres(10)).toBeCloseTo(37.8541)
+  })
+
+  test('gallonsToLitres(5) returns 18.92705', () => {
+    expect(gallonsToLitres(5)).toBeCloseTo(18.92705)
+  })
+
+  test('throws TypeError for non-number input', () => {
+    expect(() => gallonsToLitres('10')).toThrow(TypeError)
+  })
+
+  test('throws TypeError for NaN', () => {
+    expect(() => gallonsToLitres(NaN)).toThrow(TypeError)
+  })
+})