1 files changed, 69 insertions, 0 deletions
diff --git a/date-fns/src/addYears/test.ts b/date-fns/src/addYears/test.ts
new file mode 100644
index 0000000..30031f6
--- /dev/null
+++ b/date-fns/src/addYears/test.ts
@@ -0,0 +1,69 @@
+// @flow
+/* eslint-env mocha */
+
+import assert from 'assert'
+import addYears from '.'
+
+describe('addYears', function() {
+  it('adds the given number of years', function() {
+    const result = addYears(new Date(2014, 8 /* Sep */, 1), 5)
+    assert.deepStrictEqual(result, new Date(2019, 8 /* Sep */, 1))
+  })
+
+  it('accepts a timestamp', function() {
+    const result = addYears(new Date(2014, 8 /* Sep */, 1).getTime(), 12)
+    assert.deepStrictEqual(result, new Date(2026, 8 /* Sep */, 1))
+  })
+
+  it('converts a fractional number to an integer', function() {
+    const result = addYears(new Date(2014, 8 /* Sep */, 1), 5.555)
+    assert.deepStrictEqual(result, new Date(2019, 8 /* Sep */, 1))
+  })
+
+  it('implicitly converts number arguments', function() {
+    // @ts-expect-error
+    const result = addYears(new Date(2014, 8 /* Sep */, 1), '5')
+    assert.deepStrictEqual(result, new Date(2019, 8 /* Sep */, 1))
+  })
+
+  it('does not mutate the original date', function() {
+    const date = new Date(2014, 8 /* Sep */, 1)
+    addYears(date, 12)
+    assert.deepStrictEqual(date, new Date(2014, 8 /* Sep */, 1))
+  })
+
+  it('handles the leap years properly', function() {
+    const result = addYears(new Date(2016, 1 /* Feb */, 29), 1)
+    assert.deepStrictEqual(result, new Date(2017, 1 /* Feb */, 28))
+  })
+
+  it('handles dates before 100 AD', function() {
+    const initialDate = new Date(0)
+    initialDate.setFullYear(0, 1 /* Feb */, 29)
+    initialDate.setHours(0, 0, 0, 0)
+    const expectedResult = new Date(0)
+    expectedResult.setFullYear(1, 1 /* Feb */, 28)
+    expectedResult.setHours(0, 0, 0, 0)
+    const result = addYears(initialDate, 1)
+    assert.deepStrictEqual(result, expectedResult)
+  })
+
+  it('returns `Invalid Date` if the given date is invalid', function() {
+    const result = addYears(new Date(NaN), 5)
+    // @ts-expect-error
+    assert(result instanceof Date && isNaN(result))
+  })
+
+  it('returns `Invalid Date` if the given amount is NaN', function() {
+    const result = addYears(new Date(2014, 8 /* Sep */, 1), NaN)
+    // @ts-expect-error
+    assert(result instanceof Date && isNaN(result))
+  })
+
+  it('throws TypeError exception if passed less than 2 arguments', function() {
+    // @ts-expect-error
+    assert.throws(addYears.bind(null), TypeError)
+    // @ts-expect-error
+    assert.throws(addYears.bind(null, 1), TypeError)
+  })
+})