fix: validate config string formats

[Dexter2099]

Fixes #1451.

Summary

• Enable JSON Schema format checking when validating plugin configuration.
• Add regression coverage showing an invalid date-time config value raises ConfigValidationError.
• Update the shared core test tap fixture to use a valid RFC3339 date-time value for start_date.

Validation

• uv run pytest tests/core/test_tap_class.py::test_config_errors -q
• uv run pytest tests/core/test_tap_class.py tests/core/test_target_class.py tests/core/test_plugin_base.py tests/core/test_plugin_config.py tests/core/test_jsonschema_helpers.py -q
• uv run pytest tests/core -q
• pre-commit run --files singer_sdk/plugin_base.py tests/core/test_tap_class.py tests/core/conftest.py tests/core/test_streams.py
• NOX_DEFAULT_VENV_BACKEND=uv nox -rs tests-3.11 -- tests/core

Summary by Sourcery

Validate plugin configuration values against their declared JSON Schema formats.

Bug Fixes:

• Enforce JSON Schema format validation for plugin configuration values, including invalid date-time values.

Tests:

• Add regression coverage for invalid date-time configuration values and update shared test fixtures to use a valid RFC3339 timestamp.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Enables JSON Schema format checking for plugin configuration validation and updates tests/fixtures to use and assert correct RFC3339 date-time handling, including a regression test for invalid date-time values.

File-Level Changes

Change	Details	Files
Enable JSON Schema format checking during plugin configuration validation.	Update the JSONSchemaValidator instantiation to pass a format_checker so that string formats such as date-time are validated. Ensure configuration validation now yields errors when values do not conform to declared JSON Schema formats.	singer_sdk/plugin_base.py
Add regression coverage to ensure invalid date-time config values fail validation.	Extend parametrized tap config error tests with a case where start_date has an invalid date-time string. Assert that ConfigValidationError is raised and that the error message reflects the date-time format violation.	tests/core/test_tap_class.py
Align test fixtures and constants with valid RFC3339 date-time values for start_date.	Update the SimpleTestTap config fixture to use an RFC3339-compliant date-time string for start_date. Adjust the CONFIG_START_DATE constant used by stream tests to match the new RFC3339 date-time format.	tests/core/conftest.py tests/core/test_streams.py

Assessment against linked issues

Issue	Objective	Addressed	Explanation
#1451	Enable JSON Schema format keyword validation (e.g., format: "date-time") during plugin configuration validation so that incorrectly formatted strings cause a config validation error.	✅
#1451	Avoid breaking existing configurations that use a date-time JSON Schema format but provide values like "2021-01-01" (e.g., by relaxing the schema or using a union of date-time and date).	❌	The PR enables strict format checking by passing format_checker=JSONSchemaValidator.FORMAT_CHECKER to the validator but does not modify DateTimeType or schemas to allow date values as an alternative. Instead, it updates tests to use a fully RFC3339-compliant date-time string (2021-01-01T00:00:00Z), meaning existing user configs that use 2021-01-01 for a date-time field would now fail validation.

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[sourcery-ai]

Hey - I've found 1 issue, and left some high level feedback:

• The new invalid_date_time_format test asserts the exact jsonschema error string ("'not-a-date' is not a 'date-time'"), which may be brittle across jsonschema versions or implementations; consider matching on a more stable substring or pattern instead of the full message.
• Enabling format_checker changes validation behavior for existing configs that previously passed; if this is expected, consider whether there should be a way to opt out or gate this behavior for plugins that intentionally use non‑RFC3339 date strings.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The new `invalid_date_time_format` test asserts the exact jsonschema error string (`"'not-a-date' is not a 'date-time'"`), which may be brittle across jsonschema versions or implementations; consider matching on a more stable substring or pattern instead of the full message.
- Enabling `format_checker` changes validation behavior for existing configs that previously passed; if this is expected, consider whether there should be a way to opt out or gate this behavior for plugins that intentionally use non‑RFC3339 date strings.

## Individual Comments

### Comment 1
<location path="tests/core/test_streams.py" line_range="37" />
<code_context>
     from tests.core.conftest import SimpleTestTap

-CONFIG_START_DATE = "2021-01-01"
+CONFIG_START_DATE = "2021-01-01T00:00:00Z"


</code_context>
<issue_to_address>
**suggestion (testing):** Consider centralizing the test `start_date` value to avoid drift between tests and fixtures

Since this value must stay in sync with the fixture’s `start_date`, consider defining it once (e.g., as a shared fixture or constant in `conftest.py`) and importing it here. That will prevent format drift across tests and simplify future format changes.

Suggested implementation:

```python
    from singer_sdk.helpers.types import Context, Record
    from tests.core.conftest import CONFIG_START_DATE, SimpleTestTap

```

To fully implement the centralization, you should also:

1. Define `CONFIG_START_DATE = "2021-01-01T00:00:00Z"` (or whatever value you prefer) in `tests/core/conftest.py`.
2. Ensure any fixtures or helper functions in `tests/core/conftest.py` that use a start date reference this `CONFIG_START_DATE` constant so the tests and fixtures remain synchronized.
</issue_to_address>

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.36%. Comparing base (f55cc44) to head (6b29057).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3669   +/-   ##
=======================================
  Coverage   94.36%   94.36%           
=======================================
  Files          74       74           
  Lines        6296     6296           
  Branches      770      770           
=======================================
  Hits         5941     5941           
  Misses        266      266           
  Partials       89       89           

Flag	Coverage Δ
core	82.94% <100.00%> (ø)
end-to-end	75.73% <100.00%> (ø)
optional-components	45.04% <0.00%> (ø)

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[codspeed-hq]

Merging this PR will not alter performance

✅ 14 untouched benchmarks

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_{Comparing Dexter2099:codex/validate-config-string-formats (6b29057) with main (a6fcdf7)¹}

Footnotes

1. No successful run was found on main (f55cc44) during the generation of this report, so a6fcdf7 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[sourcery-ai]

Sourcery assessment

Approved.

[read-the-docs-community]

Documentation build overview

📚 Meltano SDK | 🛠️ Build #34343919 | 📁 Comparing 6b29057 against latest (bf02d4f)

  🔍 Preview build  

33 files changed · ± 33 modified

± Modified

• CONTRIBUTING.html
• batch.html
• dev_guide.html
• stream_maps.html
• typing.html
• classes/singer_sdk.BatchSink.html
• classes/singer_sdk.GraphQLStream.html
• classes/singer_sdk.InlineMapper.html
• classes/singer_sdk.RESTStream.html
• classes/singer_sdk.Sink.html
• and 23 more...