1 files changed, 52 insertions, 0 deletions
diff --git a/date-fns/src/subDays/test.ts b/date-fns/src/subDays/test.ts
new file mode 100644
index 0000000..fadc101
--- /dev/null
+++ b/date-fns/src/subDays/test.ts
@@ -0,0 +1,52 @@
+// @flow
+/* eslint-env mocha */
+
+import assert from 'power-assert'
+import subDays from '.'
+
+describe('subDays', function() {
+  it('subtracts the given number of days', function() {
+    const result = subDays(new Date(2014, 8 /* Sep */, 1), 10)
+    assert.deepEqual(result, new Date(2014, 7 /* Aug */, 22))
+  })
+
+  it('accepts a timestamp', function() {
+    const result = subDays(new Date(2014, 8 /* Sep */, 1).getTime(), 10)
+    assert.deepEqual(result, new Date(2014, 7 /* Aug */, 22))
+  })
+
+  it('converts a fractional number to an integer', function() {
+    const result = subDays(new Date(2014, 8 /* Sep */, 1), 10.85)
+    assert.deepEqual(result, new Date(2014, 7 /* Aug */, 22))
+  })
+
+  it('implicitly converts number arguments', function() {
+    // $ExpectedMistake
+    // @ts-expect-error
+    const result = subDays(new Date(2014, 8 /* Sep */, 1), '10')
+    assert.deepEqual(result, new Date(2014, 7 /* Aug */, 22))
+  })
+
+  it('does not mutate the original date', function() {
+    const date = new Date(2014, 8 /* Sep */, 1)
+    subDays(date, 11)
+    assert.deepEqual(date, new Date(2014, 8 /* Sep */, 1))
+  })
+
+  it('returns `Invalid Date` if the given date is invalid', function() {
+    const result = subDays(new Date(NaN), 10)
+    // @ts-expect-error
+    assert(result instanceof Date && isNaN(result))
+  })
+
+  it('returns `Invalid Date` if the given amount is NaN', function() {
+    const result = subDays(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() {
+    assert.throws(subDays.bind(null), TypeError)
+    assert.throws(subDays.bind(null, 1), TypeError)
+  })
+})