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

Enable strict JSON Schema format validation for plugin configuration and align tests with RFC3339-compliant date-time values.

Bug Fixes:

• Ensure configuration validation checks JSON Schema formats such as date-time when validating plugin configs.

Tests:

• Add regression coverage for invalid date-time configuration values and update core tap/stream test fixtures to use RFC3339-compliant start_date values.

[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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[sourcery-ai]

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:

    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.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.12%. Comparing base (bf02d4f) to head (245d8fc).
⚠️ Report is 22 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3669   +/-   ##
=======================================
  Coverage   94.12%   94.12%           
=======================================
  Files          73       73           
  Lines        6198     6198           
  Branches      762      762           
=======================================
  Hits         5834     5834           
  Misses        270      270           
  Partials       94       94           

Flag	Coverage Δ
core	82.94% <100.00%> (ø)
end-to-end	76.02% <100.00%> (ø)
optional-components	44.82% <0.00%> (ø)

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[codspeed-hq]

Merging this PR will not alter performance

✅ 8 untouched benchmarks

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_{Comparing Dexter2099:codex/validate-config-string-formats (245d8fc) with main (bf02d4f)}