Convert all tests to pytest

[mattsb42-aws]

A lot of the original test suite was written in unittest. Let's get all of that moved over to pytest.

Initially, this should be converting unittest.TestCase classes to pytest classes similar to what was done in #98. We can pull those methods out to stand-alone functions later if we decide we want to, but leaving them in classes will make the diffs most simpler.

I would also like to opportunistically remove some of the over-zealous mocking present in these classes where we can.

Test modules to convert:

• test/integration/test_i_aws_encrytion_sdk_client.py Migrate test_i_aws_encryption_sdk_client.py from unittet to pytest #114
• test/unit/test_aws_encryption_sdk.py Migrated "test/unit/test_aws_encryption_sdk.py" from unittest to pytest #115
• test/unit/test_defaults.py Migrate unit/test_defaults.py from unittest to pytest #116
• test/unit/test_deserialize.py Migrate unit/test_deserialize.py from unittest from pytest #117
• test/unit/test_encryption_context.py Migrate unit/test_encryption_context.py from unittest to pytest #118
• test/unit/test_providers_base_master_key.py Migrate "test/unit/test_providers_base_master_key.py" from unittest to pytest #119
• test/unit/test_providers_base_master_key_provider.py Migrate "test/unit/test_providers_base_master_key_provider.py" from unittest to pytest #120
• test/unit/test_providers_kms_master_key.py Migrate "test/unit/test_providers_kms_master_key.py" from unittest to pytest #121
• test/unit/test_providers_kms_master_key_provider.py Migrate "test/unit/test_providers_kms_master_key_provider.py" from unittest to pytest #122
• test/unit/test_providers_raw_master_key.py Migrate "test/unit/test_providers_raw_master_key.py" from unittest to pytest #123
• test/unit/test_providers_raw_master_key_provider.py Migrate "test/unit/test_providers_raw_master_key_provider.py" from unittest to pytest #124
• test/unit/test_serialize.py Migrate "test/unit/test_serialize.py" from unittest to pytest #125
• test/unit/test_streaming_client_stream_decryptor.py Migrate "test/unit/test_streaming_client_stream_decryptor.py" from unittest to pytest #126
• test/unit/test_streaming_client_stream_encryptor.py Migrate unit/test_streaming_client_stream_encryptor.py from unittest to pytest #127
• test/unit/test_util_str_ops.py Migrate unit/test_util_str_ops.py from unittest to pytest #128
• test/unit/test_utils.py Migrate unit/test_utils.py from unittest to pytest #129

Due to the changes that will need to happen, anyone looking at this please follow the following guidelines:

1. Convert from unittest classes to classes using pytest first. We can change to functions later if desired, but converting the classes directly will minimize the changes in each test file.
2. One test file per PR. This will minimize the amount of changes that need to be reviewed and speed up the review process.
3. Run tox -re autoformat before committing to apply our formatting rules.

[ansanper]

Hello! I can help with this issue, I will start working on it.

[mattsb42-aws]

Hi, @AndresSan6. That would be awesome, thanks! We would love any help you want to contribute.

One thing I would ask, since we haven't gotten around to setting up pre-commit hooks yet: please make sure you run tox -re autoformat before each commit (or at least before submitting the PR). This applies black and isort to the codebase.