1 files changed, 34 insertions, 0 deletions
diff --git a/date-fns/src/lastDayOfDecade/test.ts b/date-fns/src/lastDayOfDecade/test.ts
new file mode 100644
index 0000000..75c241e
--- /dev/null
+++ b/date-fns/src/lastDayOfDecade/test.ts
@@ -0,0 +1,34 @@
+// @flow
+/* eslint-env mocha */
+
+import assert from 'power-assert'
+import lastDayOfDecade from '.'
+
+describe('lastDayOfDecade', function() {
+  it('returns the date with the time set to 00:00:00 and the date set to the last day of a decade', function() {
+    const date = new Date(1985, 9 /* Oct */, 20)
+    const result = lastDayOfDecade(date)
+    assert.deepEqual(result, new Date(1989, 11 /* Dec */, 31))
+  })
+
+  it('accepts a timestamp', function() {
+    const date = new Date(1975, 0 /* Jan */, 19).getTime()
+    const result = lastDayOfDecade(date)
+    assert.deepEqual(result, new Date(1979, 11 /* Dec */, 31))
+  })
+
+  it('does not mutate the original date', function() {
+    const date = new Date(2013, 3 /* Apr */, 23)
+    lastDayOfDecade(date)
+    assert.deepEqual(date, new Date(2013, 3 /* Apr */, 23))
+  })
+
+  it('returns `Invalid Date` if the given date is invalid', function() {
+    const result = lastDayOfDecade(new Date(NaN))
+    assert(result instanceof Date && isNaN(result.getTime()))
+  })
+
+  it('throws TypeError exception if passed less than 1 argument', function() {
+    assert.throws(lastDayOfDecade.bind(null), TypeError)
+  })
+})