Add HaveMillisecond/NotHaveMillisecond assertion methods for DateTime and DateTimeOffset by Copilot · Pull Request #3164 · fluentassertions/fluentassertions

Copilot · 2026-02-28T18:25:14Z

Implementation Complete ✓

Summary

Successfully implemented HaveMillisecond and NotHaveMillisecond assertion methods for both DateTime and DateTimeOffset types, following the existing patterns. All tests pass successfully with no regressions detected. Test naming has been refined to follow clean naming conventions without rigid and noisy words.

Original prompt

This section details on the original issue you should resolve

<issue_title>Method to assert the millisecond part of a DateTime / DateTimeOffset instance</issue_title>
<issue_description>### Background and motivation

Currently, FluentAssertions has methods to assert the year, month, day, hour, minute, second and offset of a DateTimeOffset (HaveX), but an equivalent method for the millisecond part is missing. Generally, it would be nice to assert the millisecond part in the style of FluentAssertions instead of using result.Millisecond.Should().Be(milliseconds).

I'm currently working on a library that provides convenience methods based on DateTime/DateTimeOffset and implement date and time related unit tests for it.

This is very easy to implement, because we can extend the DateTimeAssertions class and DateTimeOffsetAssertions class by a method called HaveMillisecond.

The implementation of this method could look like following:

public AndConstraint<DateTimeOffsetAssertions> HaveMillisecond(int expectedMilliseconds, string because = "", params object[] becauseArgs)
{
    Execute.Assertion
      .ForCondition(this.Subject != null)
      .BecauseOf(because, becauseArgs)
      .FailWith("Expected {context:DateTimeOffset} to have milliseconds {0}{reason}, but found <null>.", expectedMilliseconds);

    Execute.Assertion
      .ForCondition(this.Subject!.Value.Millisecond == expectedMilliseconds)
      .BecauseOf(because, becauseArgs)
      .FailWith("Expected {context:DateTimeOffset} to have milliseconds {0}{reason}, but found {1}.", expectedMilliseconds, this.Subject.Value.Millisecond);

    return new AndConstraint<DateTimeOffsetAssertions>(this);
}

Also the opponent of HaveMillisecond, which would be NotHaveMillisecond, can be implemented this way by inverting / changing the condition to this.Subject!.Value.Millisecond != expectedMilliseconds.

API Proposal

public class DateTimeOffsetAssertions<TAssertions>
{
    public AndConstraint<DateTimeOffsetAssertions> HaveMillisecond(int expectedMilliseconds, string because = "", params object[] becauseArgs);
    public AndConstraint<DateTimeOffsetAssertions> NotHaveMillisecond(int expectedMilliseconds, string because = "", params object[] becauseArgs);
}

public class DateTimeAssertions<TAssertions>
{
    public AndConstraint<DateTimeAssertions> HaveMillisecond(int expectedMilliseconds, string because = "", params object[] becauseArgs);
    public AndConstraint<DateTimeAssertions> NotHaveMillisecond(int expectedMilliseconds, string because = "", params object[] becauseArgs);
}

API Usage

var dateTimeOffset = DateTimeOffset.Parse("2024-08-23T00:00:00.123+00:00");
dateTimeOffset.Should().HaveMilliseconds(123);
dateTimeOffset.Should().NotHaveMilliseconds(124);

Alternative Designs

Alternately, you could write an extension method based on DateTimeOffsetAssertions class and add there the HaveMillisecond method. This would not directly change the API of FluentAssertions, but would not be consistent with the rest of the DateTime/DateTimeOffset method provided by FluentAssertions.

The extension method could be implemented like following:

internal static class DateTimeOffsetAssertionsExtensions
{
    internal static FluentAssertions.Primitives.DateTimeOffsetAssertions HaveMillisecond(
        this FluentAssertions.Primitives.DateTimeOffsetAssertions assertions,
        int expectedMilliseconds,
        string because = "",
        params object[] becauseArgs)
        {
            var subject = assertions.Subject;
            Execute.Assertion
                .ForCondition(subject != null)
                .BecauseOf(because, becauseArgs)
                .FailWith("Expected {context:DateTimeOffset} to have milliseconds {0}{reason}, but found <null>.", expectedMilliseconds);

            Execute.Assertion
                .ForCondition(subject!.Value.Millisecond == expectedMilliseconds)
                .BecauseOf(because, becauseArgs)
                .FailWith("Expected {context:DateTimeOffset} to have milliseconds {0}{reason}, but found {1}.", expectedMilliseconds, subject.Value.Millisecond);

            return assertions;
        }
}

Risks

None, because it adds an extra method to assert the millisecond part of a DateTime / DateTimeOffset instance.

Are you willing to help with a proof-of-concept (as PR in that or a separate repo) first and as pull-request later on?

Yes, please assign this issue to me.</issue_description>

Comments on the Issue (you are @copilot ...

Fixes Method to assert the millisecond part of a DateTime / DateTimeOffset instance #2738

🔒 GitHub Advanced Security automatically protects Copilot coding agent pull requests. You can protect all pull requests by enabling Advanced Security for your repositories. Learn more about Advanced Security.

Co-authored-by: jnyrup <[email protected]>

github-actions · 2026-03-03T11:55:55Z

Test Results

37 files ± 0 37 suites ±0 6m 26s ⏱️ -23s
6 309 tests +12 6 308 ✅ +12 1 💤 ±0 0 ❌ ±0
39 200 runs +72 39 194 ✅ +72 6 💤 ±0 0 ❌ ±0

Results for commit eee7305. ± Comparison against base commit 27bd2f9.

This pull request removes 10 and adds 20 tests. Note that renamed tests count towards both.

FluentAssertions.Specs.Streams.StreamAssertionSpecs+HaveLength ‑ When_a_throwing_stream_should_have_a_length_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
FluentAssertions.Specs.Streams.StreamAssertionSpecs+HaveLength ‑ When_a_throwing_stream_should_have_a_length_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
FluentAssertions.Specs.Streams.StreamAssertionSpecs+HavePosition ‑ When_a_throwing_stream_should_have_a_position_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
FluentAssertions.Specs.Streams.StreamAssertionSpecs+HavePosition ‑ When_a_throwing_stream_should_have_a_position_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
FluentAssertions.Specs.Streams.StreamAssertionSpecs+NotHaveLength ‑ When_a_throwing_stream_should_not_have_a_length_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
FluentAssertions.Specs.Streams.StreamAssertionSpecs+NotHaveLength ‑ When_a_throwing_stream_should_not_have_a_length_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
FluentAssertions.Specs.Streams.StreamAssertionSpecs+NotHavePosition ‑ When_a_throwing_stream_should_not_have_a_position_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
FluentAssertions.Specs.Streams.StreamAssertionSpecs+NotHavePosition ‑ When_a_throwing_stream_should_not_have_a_position_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'GetLengthExceptionMessage'.)
Object name: 'GetPositionExceptionMessage'.)

FluentAssertions.Specs.Primitives.DateTimeAssertionSpecs+HaveMillisecond ‑ Fails_for_datetime_with_different_milliseconds
FluentAssertions.Specs.Primitives.DateTimeAssertionSpecs+HaveMillisecond ‑ Fails_for_null_datetime
FluentAssertions.Specs.Primitives.DateTimeAssertionSpecs+HaveMillisecond ‑ Succeeds_for_datetime_with_the_same_milliseconds
FluentAssertions.Specs.Primitives.DateTimeAssertionSpecs+NotHaveMillisecond ‑ Fails_for_datetime_with_the_same_milliseconds
FluentAssertions.Specs.Primitives.DateTimeAssertionSpecs+NotHaveMillisecond ‑ Fails_for_null_datetime
FluentAssertions.Specs.Primitives.DateTimeAssertionSpecs+NotHaveMillisecond ‑ Succeeds_for_datetime_with_different_milliseconds
FluentAssertions.Specs.Primitives.DateTimeOffsetAssertionSpecs+HaveMillisecond ‑ Fails_for_datetimeoffset_with_different_milliseconds
FluentAssertions.Specs.Primitives.DateTimeOffsetAssertionSpecs+HaveMillisecond ‑ Fails_for_null_datetimeoffset
FluentAssertions.Specs.Primitives.DateTimeOffsetAssertionSpecs+HaveMillisecond ‑ Succeeds_for_datetimeoffset_with_the_same_milliseconds
FluentAssertions.Specs.Primitives.DateTimeOffsetAssertionSpecs+NotHaveMillisecond ‑ Fails_for_datetimeoffset_with_the_same_milliseconds
…

♻️ This comment has been updated with latest results.

github-actions · 2026-03-03T11:59:23Z

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jnyrup

@copilot please address the following points:

Update docs/_pages/releases.md to include a sub-item under "What's New" succiently summarizing the feature added in this PR
Run either of AcceptApiChanges.sh or AcceptApiChanges.ps1 to updates the approved API.
Update the naming of the added test methods to the folllow the new naming convention.
See e.g. Tests/FluentAssertions.Specs/Numeric/NumericAssertionSpecs.BeNaN.cs

dennisdoomen · 2026-03-05T06:09:21Z

@copilot please address the following points:

Update docs/_pages/releases.md to include a sub-item under "What's New" succiently summarizing the feature added in this PR

Run either of AcceptApiChanges.sh or AcceptApiChanges.ps1 to updates the approved API.

Update the naming of the added test methods to the folllow the new naming convention.

See e.g. Tests/FluentAssertions.Specs/Numeric/NumericAssertionSpecs.BeNaN.cs

@copilot apply the requested changes

…nges Co-authored-by: dennisdoomen <[email protected]>

Copilot · 2026-03-05T06:14:01Z

@copilot please address the following points:

Update docs/_pages/releases.md to include a sub-item under "What's New" succiently summarizing the feature added in this PR
...

All requested changes have been applied in commit fcb2dfc:

✅ Updated docs/_pages/releases.md with feature summary
✅ Ran AcceptApiChanges.sh to update approved API for all target frameworks (net47, net6.0, netstandard2.0, netstandard2.1)
✅ Updated test method naming to follow the new convention (e.g., Milliseconds_are_asserted_when_values_match instead of When_asserting_subject_datetime_should_have_milliseconds_with_the_same_value_it_should_succeed)

All tests pass: 18 HaveMillisecond tests, 4 approval tests, and no regressions in existing DateTime/DateTimeOffset tests.

coveralls · 2026-03-05T08:27:43Z

Pull Request Test Coverage Report for Build 22803252634

Details

37 of 37 (100.0%) changed or added relevant lines in 2 files are covered.
No unchanged relevant lines lost coverage.
Overall coverage increased (+0.006%) to 97.174%

Totals
Change from base Build 22318656339:	0.006%
Covered Lines:	12999
Relevant Lines:	13223

💛 - Coveralls

Tests/FluentAssertions.Specs/Primitives/DateTimeAssertionSpecs.HaveMillisecond.cs

Co-authored-by: dennisdoomen <[email protected]>

Initial plan

210b6fa

Copilot AI assigned Copilot and jnyrup Feb 28, 2026

Copilot started work on behalf of jnyrup February 28, 2026 18:25 View session

Add HaveMillisecond and NotHaveMillisecond methods with tests

0007da3

Co-authored-by: jnyrup <[email protected]>

Copilot AI changed the title ~~[WIP] Add method to assert millisecond part of DateTimeOffset~~ Add HaveMillisecond/NotHaveMillisecond assertion methods for DateTime and DateTimeOffset Feb 28, 2026

Copilot finished work on behalf of jnyrup February 28, 2026 18:35

jnyrup requested changes Mar 4, 2026

View reviewed changes

Copilot started work on behalf of dennisdoomen March 5, 2026 06:09 View session

Address PR feedback: update releases.md, rename tests, accept API cha…

fcb2dfc

…nges Co-authored-by: dennisdoomen <[email protected]>

Copilot finished work on behalf of dennisdoomen March 5, 2026 06:14

jnyrup marked this pull request as ready for review March 5, 2026 08:49

jnyrup reviewed Mar 5, 2026

View reviewed changes

Tests/FluentAssertions.Specs/Primitives/DateTimeAssertionSpecs.HaveMillisecond.cs Show resolved Hide resolved

Copilot started work on behalf of dennisdoomen March 7, 2026 16:58 View session

Remove noisy words from test names (should, when)

eee7305

Co-authored-by: dennisdoomen <[email protected]>

Copilot finished work on behalf of dennisdoomen March 7, 2026 17:01

jnyrup approved these changes Mar 7, 2026

View reviewed changes

jnyrup requested a review from dennisdoomen March 7, 2026 17:20

jnyrup added this to the 8.9 milestone Mar 7, 2026

dennisdoomen approved these changes Mar 8, 2026

View reviewed changes

dennisdoomen added the enhancement label Mar 8, 2026

dennisdoomen merged commit ef3a1e0 into main Mar 8, 2026
14 checks passed

dennisdoomen deleted the copilot/add-millisecond-assertion branch March 8, 2026 07:00

This was referenced Mar 16, 2026

Bump FluentAssertions from 8.8.0 to 8.9.0 GuilhermeStracini/apiclient-boilerplate-dotnet#423

Merged

Bump FluentAssertions from 8.8.0 to 8.9.0 GuilhermeStracini/POC-dotnet-template#210

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Add HaveMillisecond/NotHaveMillisecond assertion methods for DateTime and DateTimeOffset#3164

Add HaveMillisecond/NotHaveMillisecond assertion methods for DateTime and DateTimeOffset#3164
dennisdoomen merged 4 commits intomainfrom
copilot/add-millisecond-assertion

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Implementation Complete ✓

Summary

API Proposal

API Usage

Alternative Designs

Risks

Are you willing to help with a proof-of-concept (as PR in that or a separate repo) first and as pull-request later on?

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