1 files changed, 67 insertions, 0 deletions
diff --git a/date-fns/src/subMilliseconds/test.ts b/date-fns/src/subMilliseconds/test.ts
new file mode 100644
index 0000000..bd93b39
--- /dev/null
+++ b/date-fns/src/subMilliseconds/test.ts
@@ -0,0 +1,67 @@
+// @flow
+/* eslint-env mocha */
+
+import assert from 'power-assert'
+import subMilliseconds from '.'
+
+describe('subMilliseconds', function() {
+  it('subtracts the given number of milliseconds', function() {
+    const result = subMilliseconds(
+      new Date(2014, 6 /* Jul */, 10, 12, 45, 30, 0),
+      750
+    )
+    assert.deepEqual(result, new Date(2014, 6 /* Jul */, 10, 12, 45, 29, 250))
+  })
+
+  it('accepts a timestamp', function() {
+    const result = subMilliseconds(
+      new Date(2014, 6 /* Jul */, 10, 12, 45, 30, 0).getTime(),
+      500
+    )
+    assert.deepEqual(result, new Date(2014, 6 /* Jul */, 10, 12, 45, 29, 500))
+  })
+
+  it('converts a fractional number to an integer', function() {
+    const result = subMilliseconds(
+      new Date(2014, 6 /* Jul */, 10, 12, 45, 30, 0),
+      750.75
+    )
+    assert.deepEqual(result, new Date(2014, 6 /* Jul */, 10, 12, 45, 29, 250))
+  })
+
+  it('implicitly converts number arguments', function() {
+    const result = subMilliseconds(
+      new Date(2014, 6 /* Jul */, 10, 12, 45, 30, 0),
+      // $ExpectedMistake
+      // @ts-expect-error
+      '750'
+    )
+    assert.deepEqual(result, new Date(2014, 6 /* Jul */, 10, 12, 45, 29, 250))
+  })
+
+  it('does not mutate the original date', function() {
+    const date = new Date(2014, 6 /* Jul */, 10, 12, 45, 30, 0)
+    subMilliseconds(date, 250)
+    assert.deepEqual(date, new Date(2014, 6 /* Jul */, 10, 12, 45, 30, 0))
+  })
+
+  it('returns `Invalid Date` if the given date is invalid', function() {
+    const result = subMilliseconds(new Date(NaN), 750)
+    // @ts-expect-error
+    assert(result instanceof Date && isNaN(result))
+  })
+
+  it('returns `Invalid Date` if the given amount is NaN', function() {
+    const result = subMilliseconds(
+      new Date(2014, 6 /* Jul */, 10, 12, 45, 30, 0),
+      NaN
+    )
+    // @ts-expect-error
+    assert(result instanceof Date && isNaN(result))
+  })
+
+  it('throws TypeError exception if passed less than 2 arguments', function() {
+    assert.throws(subMilliseconds.bind(null), TypeError)
+    assert.throws(subMilliseconds.bind(null, 1), TypeError)
+  })
+})