🎉Source Sendgrid: increase unit test coverage at least 90%

[lazebnyi]

What

#16331

How

Added unit tests

Pre-merge Checklist

Updating a connector

Community member or Airbyter

• Grant edit access to maintainers (instructions)
• Secrets in the connector's spec are annotated with airbyte_secret
• Unit & integration tests added and passing. Community members, please provide proof of success locally e.g: screenshot or copy-paste unit, integration, and acceptance test output. To run acceptance tests for a Python connector, follow instructions in the README. For java connectors run ./gradlew :airbyte-integrations:connectors:<name>:integrationTest.
• Code reviews completed
• Documentation updated
  • Connector's README.md
  • Connector's bootstrap.md. See description and examples
  • Changelog updated in docs/integrations/<source or destination>/<name>.md including changelog. See changelog example
• PR name follows PR naming conventions

[lazebnyi]

/test connector=connectors/source-sendgrid

🕑 connectors/source-sendgrid https://github.com/airbytehq/airbyte/actions/runs/2993358696
❌ connectors/source-sendgrid https://github.com/airbytehq/airbyte/actions/runs/2993358696
🐛 https://gradle.com/s/rjatgyarzom6s

Build Failed

Test summary info:

	 =========================== short test summary info ============================
	 ERROR unit_tests/unit_test.py::test_read_records[Templates-https:/api.sendgrid.com/v3/templates-expected0]
	 ERROR unit_tests/unit_test.py::test_read_records[Lists-https:/api.sendgrid.com/v3/marketing/lists-expected1]
	 ERROR unit_tests/unit_test.py::test_read_records[Campaigns-https:/api.sendgrid.com/v3/marketing/campaigns-expected2]
	 ERROR unit_tests/unit_test.py::test_read_records[Contacts-https:/api.sendgrid.com/v3/marketing/contacts-expected3]
	 ERROR unit_tests/unit_test.py::test_read_records[Segments-https:/api.sendgrid.com/v3/marketing/segments-expected4]
	 ERROR unit_tests/unit_test.py::test_read_records[Blocks-https:/api.sendgrid.com/v3/suppression/blocks-expected5]
	 ERROR unit_tests/unit_test.py::test_read_records[SuppressionGroupMembers-https:/api.sendgrid.com/v3/asm/suppressions-expected6]
	 ERROR unit_tests/unit_test.py::test_read_records[SuppressionGroups-https:/api.sendgrid.com/v3/asm/groups-expected7]
	 ERROR unit_tests/unit_test.py::test_read_records[GlobalSuppressions-https:/api.sendgrid.com/v3/suppression/unsubscribes-expected8]
	 �[31m=================== �[32m6 passed�[0m, �[33m45 warnings�[0m, �[31m�[1m9 errors�[0m�[31m in 0.71s�[0m�[31m ===================�[0m

[bazarnov]

I think the requests_mock should be the part of setup.py, since unit_tests require it.
https://github.com/airbytehq/airbyte/blob/lazebnyi/source-sendgrid-coverage-unittest/airbyte-integrations/connectors/source-sendgrid/setup.py

[lazebnyi]

/test connector=connectors/source-sendgrid

🕑 connectors/source-sendgrid https://github.com/airbytehq/airbyte/actions/runs/2994449438
❌ connectors/source-sendgrid https://github.com/airbytehq/airbyte/actions/runs/2994449438
🐛 https://gradle.com/s/vwfcblkgbb3wc

Build Failed

Test summary info:

Could not find result summary

[lazebnyi]

/test connector=connectors/source-sendgrid

🕑 connectors/source-sendgrid https://github.com/airbytehq/airbyte/actions/runs/2994611511
❌ connectors/source-sendgrid https://github.com/airbytehq/airbyte/actions/runs/2994611511
🐛 https://gradle.com/s/yvtcr72hplfag

Build Failed

Test summary info:

=========================== short test summary info ============================
FAILED test_core.py::TestBasicRead::test_read[inputs0] - Failed: Stream campa...
======================== 1 failed, 28 passed in 58.60s =========================

[lazebnyi]

/test connector=connectors/source-sendgrid

🕑 connectors/source-sendgrid https://github.com/airbytehq/airbyte/actions/runs/2994883571
✅ connectors/source-sendgrid https://github.com/airbytehq/airbyte/actions/runs/2994883571
Python tests coverage:

Name                          Stmts   Miss  Cover
-------------------------------------------------
source_sendgrid/__init__.py       2      0   100%
source_sendgrid/source.py        19      1    95%
source_sendgrid/streams.py      158     17    89%
-------------------------------------------------
TOTAL                           179     18    90%
	 Name                                                 Stmts   Miss  Cover   Missing
	 ----------------------------------------------------------------------------------
	 source_acceptance_test/base.py                          10      4    60%   15-18
	 source_acceptance_test/config.py                        83      6    93%   78-80, 84-86
	 source_acceptance_test/conftest.py                     164    164     0%   6-282
	 source_acceptance_test/plugin.py                        48     48     0%   6-104
	 source_acceptance_test/tests/test_core.py              329    111    66%   39, 50-58, 63-70, 74-75, 79-80, 164, 202-219, 228-236, 240-245, 251, 284-289, 327-334, 374-376, 379, 439-448, 477-478, 484, 487, 520-530, 543-568, 573-577
	 source_acceptance_test/tests/test_full_refresh.py       52      2    96%   34, 65
	 source_acceptance_test/tests/test_incremental.py       121     25    79%   21-23, 29-31, 36-43, 48-61, 208-216
	 source_acceptance_test/utils/asserts.py                 37      2    95%   57-58
	 source_acceptance_test/utils/common.py                  77     17    78%   15-16, 24-30, 47-54, 64, 67
	 source_acceptance_test/utils/compare.py                 62     23    63%   21-51, 68, 97-99
	 source_acceptance_test/utils/connector_runner.py       110     48    56%   23-26, 32, 36, 39-64, 67-69, 72-74, 77-79, 82-84, 87-89, 92-110, 144-146
	 source_acceptance_test/utils/json_schema_helper.py     105     13    88%   30-31, 38, 41, 65-68, 96, 120, 190-192
	 ----------------------------------------------------------------------------------
	 TOTAL                                                 1322    463    65%

Build Passed

Test summary info:

All Passed