fix(ci_visibility): only enable coverage if test skipping is enabled (#7564)

Prevents enabling coverage (and using the `coverage` module) when using
the unittest integration if the Intelligent Test Runner is not enabled.
The `coverage` module is not a required dependency for CI Visibility
(only for ITR) and shouldn't be assumed to be available and installed.
 
## Checklist

- [x] Change(s) are motivated and described in the PR description.
- [x] Testing strategy is described if automated tests are not included
in the PR.
- [x] Risk is outlined (performance impact, potential for breakage,
maintainability, etc).
- [x] Change is maintainable (easy to change, telemetry, documentation).
- [x] [Library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
are followed. If no release note is required, add label
`changelog/no-changelog`.
- [x] Documentation is included (in-code, generated user docs, [public
corp docs](https://github.com/DataDog/documentation/)).
- [x] Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist

- [x] Title is accurate.
- [x] No unnecessary changes are introduced.
- [x] Description motivates each change.
- [x] Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes unless absolutely necessary.
- [x] Testing strategy adequately addresses listed risk(s).
- [x] Change is maintainable (easy to change, telemetry, documentation).
- [x] Release note makes sense to a user of the library.
- [x] Reviewer has explicitly acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment.
- [x] Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)
- [x] If this PR touches code that signs or publishes builds or
packages, or handles credentials of any kind, I've requested a review
from `@DataDog/security-design-and-guidance`.
- [x] This PR doesn't touch any of that.

Author: romainkomorn-exdatadog

ddtrace/contrib/unittest/patch.py

@@ -601,8 +601,9 @@ def handle_test_wrapper(func, instance, args: tuple, kwargs: dict):
                 )
                 result.stopTest(test=instance)
             else:
-                coverage = _start_coverage(root_directory)
-                instance._coverage = coverage
+                if _CIVisibility._instance._collect_coverage_enabled:
+                    coverage = _start_coverage(root_directory)
+                    instance._coverage = coverage
                 result = func(*args, **kwargs)
             _update_status_item(test_suite_span, span.get_tag(test.STATUS))
             if hasattr(instance, "_coverage"):

releasenotes/notes/ci_visibility-fix-unittest-only-enable-coverage-when-skipping-tests-1ea3d31a818277ae.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    CI Visibility: fixes a crash where the unittest integration would try to enable coverage when tests are run even
+    if the Intelligent Test Runner is not enabled.

tests/snapshots/tests.contrib.unittest_plugin.test_unittest_snapshot.test_unittest_generates_source_file_data.json

@@ -131,7 +131,6 @@
                "span.kind": "test",
                "test.class_hierarchy": "CoverageTestCase",
                "test.command": "python -m unittest",
-               "test.coverage": "{\"files\": [{\"filename\": \"test_source_file.py\", \"segments\": [[5, 0, 6, 0, -1]]}, {\"filename\": \"lib_fn.py\", \"segments\": [[1, 0, 2, 0, -1]]}]}",
                "test.framework": "unittest",
                "test.framework_version": "3.10.11",
                "test.module": "test_source_file",
@@ -174,7 +173,6 @@
                "span.kind": "test",
                "test.class_hierarchy": "CoverageTestCase",
                "test.command": "python -m unittest",
-               "test.coverage": "{\"files\": [{\"filename\": \"test_source_file.py\", \"segments\": [[8, 0, 9, 0, -1]]}, {\"filename\": \"ret_false.py\", \"segments\": [[1, 0, 2, 0, -1]]}]}",
                "test.framework": "unittest",
                "test.framework_version": "3.10.11",
                "test.module": "test_source_file",
@@ -221,7 +219,6 @@
                "span.kind": "test",
                "test.class_hierarchy": "CoverageTestCase",
                "test.command": "python -m unittest",
-               "test.coverage": "{\"files\": [{\"filename\": \"test_source_file.py\", \"segments\": [[11, 0, 12, 0, -1]]}, {\"filename\": \"ret_false.py\", \"segments\": [[2, 0, 2, 0, -1]]}]}",
                "test.framework": "unittest",
                "test.framework_version": "3.10.11",
                "test.module": "test_source_file",