[Retiarii] Fix unit test (#3064)

test/ut/__init__.py

+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT license.
+
 """
 Unit test of NNI Python modules.
 
 Test cases of each module should be placed at same path of their source files.
-For example if `nni/tool/annotation` has one test case, it should be placed at `test/ut/tool/annotation.py`;
+For example if `nni/tool/annotation` has one test case, it should be placed at `test/ut/tool/test_annotation.py`;
 if it has multiple test cases, they should be placed in `test/ut/tool/annotation/` directory.
 
 "Legacy" test cases carried from NNI v1.x might not follow above convention:
 
   + Directory `sdk` contains old test cases previously in `src/sdk/pynni/tests`.
-  + Directory `tools/cmd` contains old test cases previously in `tools/cmd/tests`.
+  + Directory `tools/nnictl` contains old test cases previously in `tools/nni_cmd/tests`.
   + Directory `tools/annotation` contains old test cases previously in `tools/nni_annotation`.
   + Directory `tools/trial_tool` contains old test cases previously in `tools/nni_trial_tool/test`.
 """
+
+import os
+
+os.environ['NNI_PLATFORM'] = 'unittest'
+os.environ['NNI_TRIAL_JOB_ID'] = 'test_trial_job_id'