Locale-sensitive datetime formatting causes test failures on non-US locales

[jasontaylordev]

Describe the bug

Description

The test suite in SagaDiagram.spec.ts compares rendered date-time strings against hard-coded values (e.g., "3/28/2025 3:04:05 AM"), assuming a US locale (en-US). However, when running the tests on systems with different locale settings such as en-AU, the default string formatting of Date.toLocaleString() results in different formats (e.g., "28/03/2025 3:04:05 am"), causing assertions to fail.

Expected behavior

Tests should pass consistently across all environments, regardless of the system or runtime locale. Date formatting in tests should either:

• Be explicitly formatted in a locale-agnostic way (e.g., using toISOString()), or
• Use a fixed locale explicitly in the component or test code (e.g., toLocaleString("en-US", options)).

Actual behavior

Tests fail in environments with non-US locales due to mismatched date formats in rendered output vs. expected values.

Steps to reproduce

1. Set your system or Node.js locale to en-AU
2. Run the test suite (SagaDiagram.spec.ts).
3. Observe test failures due to mismatched date formats.

Relevant log output

Example failures:

 FAIL  src/components/messages/SagaDiagram.spec.ts > Feature: 3 Visual Representation of Saga Timeline > Rule: 3.3 Display a chronological timeline of saga events in PST. > EXAMPLE: Rendering a Saga with 4 changes
AssertionError: expected [ '27/03/2025 8:04:05 pm', …(3) ] to deeply equal [ '3/27/2025 8:04:05 PM', …(3) ]

- Expected
+ Received

  [
-   "3/27/2025 8:04:05 PM",
-   "3/27/2025 8:04:06 PM",
-   "3/27/2025 8:04:07 PM",
-   "3/27/2025 8:04:08 PM",
+   "27/03/2025 8:04:05 pm",
+   "27/03/2025 8:04:06 pm",
+   "27/03/2025 8:04:07 pm",
+   "27/03/2025 8:04:08 pm",
  ]


 FAIL  src/components/messages/SagaDiagram.spec.ts > Feature: 3 Visual Representation of Saga Timeline > Rule: 3.2 Display a chronological timeline of saga events in UTC. > EXAMPLE: Rendering a Saga with 4 changes
AssertionError: expected [ '28/03/2025 3:04:05 am', …(3) ] to deeply equal [ '3/28/2025 3:04:05 AM', …(3) ]

- Expected
+ Received

  [
-   "3/28/2025 3:04:05 AM",
-   "3/28/2025 3:04:06 AM",
-   "3/28/2025 3:04:07 AM",
-   "3/28/2025 3:04:08 AM",
+   "28/03/2025 3:04:05 am",
+   "28/03/2025 3:04:06 am",
+   "28/03/2025 3:04:07 am",
+   "28/03/2025 3:04:08 am",
  ]

Additional Information

Workarounds

N/A

Possible solutions

Update the toLocalDateTimeString function in formatUtils.ts to accept an optional locale parameter. This allows tests to explicitly specify a locale (e.g. "en-US") to ensure consistent output across environments.

Additional information

• The issue is environment-specific and may only surface when running tests locally on machines with non-en-US locales, such as en-AU, en-GB, or other regional settings.
• The test environment (e.g., GitHub Actions) likely defaults to en-US, which is why this bug may go unnoticed in CI pipelines.
• Relying on Date.toLocaleString() without specifying a locale introduces flakiness in both tests and UI consistency across different user systems.