Add section on asserting time args for jobs

1 files changed, 19 insertions, 0 deletions

diff --git a/guides/source/testing.md b/guides/source/testing.md
index 93372b5c26..04f0297480 100644
--- a/guides/source/testing.md
+++ b/guides/source/testing.md
@@ -1733,6 +1733,25 @@ class ProductTest < ActiveSupport::TestCase
 end
 ```
 
+### Asserting Time Arguments in Jobs
+
+When serializing job arguments, `Time`, `DateTime`, and `ActiveSupport::TimeWithZone` lose microsecond precision. This means comparing deserialized time with actual time doesn't always work. To compensate for the loss of precision, `assert_enqueued_with` and `assert_performed_with` will remove microseconds from time objects in argument assertions.
+
+```ruby
+require 'test_helper'
+
+class ProductTest < ActiveSupport::TestCase
+  include ActiveJob::TestHelper
+
+  test 'that product is reserved at a given time' do
+    now = Time.now
+    assert_performed_with(job: ReservationJob, args: [product, now]) do
+      product.reserve(now)
+    end
+  end
+end
+```
+
 Testing Action Cable
 --------------------