Apply tf dev override in unit test

Author: iyabchen

Makefile

@@ -5,7 +5,10 @@ build:
 	GO111MODULE=on go build -o ${build_dir}/tfplan2cai ./cmd/tfplan2cai
 
 test:
-	GO111MODULE=on go test -short ./...
+	go version
+	terraform --version
+	./config-tf-dev-override.sh
+	TF_CLI_CONFIG_FILE="${PWD}/${TF_CONFIG_FILE}" GO111MODULE=on go test -short ./...
 
 test-integration:
 	go version

docs/contributing/index.md

@@ -1,6 +1,7 @@
 # Contributing
 
-If you want to contribute to Terraform Google Conversion, check out the [contribution guidelines](../../CONTRIBUTING.md)
+If you want to contribute to Terraform Google Conversion, check out the
+[contribution guidelines](../../CONTRIBUTING.md)
 
 ## Table of Contents
 
@@ -11,23 +12,21 @@ If you want to contribute to Terraform Google Conversion, check out the [contrib
     - [Integration Test](#integration-test)
     - [Add a new resource](#add-a-new-resource)
 
-
 ## Testing
 
-### Unit Test
-```bash
-# Unit tests
-make test
-```
+The read test(one of the unit tests) and integration test installs the provider
+binary and creates a terraform dev override file tf-dev-override.tfrc.
+[Dev override](https://googlecloudplatform.github.io/magic-modules/develop/run-tests/#optional-test-manually)
+is to make sure the test runs against the provider version specified in the go
+module. You can place your own config to point to a different go binary
+destination within tf-dev-override.tfrc. If the file already exists, it will not
+be overwritten.
 
-### Integration Test
+It is better to run both the unit test and integration tests inside a Docker
+container to match the CI/CD pipeline.
 
 **Note:** Integration tests require a test project.
 
-It is better to run the integration tests inside a Docker container to match the CI/CD pipeline.
-
-The integration test installs the provider binary and creates a terraform dev override file tf-dev-override.tfrc. [Dev override](https://googlecloudplatform.github.io/magic-modules/develop/run-tests/#optional-test-manually) is to make sure the test runs against the provider version specified in the go module. You can place your own config within tf-dev-override.tfrc. If the file already exists, it will not be overwritten.
-
 ```bash
 # Integration tests (interacts with real APIs)
 
@@ -38,13 +37,27 @@ export TEST_CREDENTIALS=~/.config/gcloud/application_default_credentials.json
 
 # Spin up a docker container to run tests.
 make run-docker
+```
+
+### Unit Test
 
+The read test(tfplan2cai/test/read_test.go) runs terraform binary to generate
+`.tfplan.json` files. It requires gcloud credential during that process.
+
+```bash
+# Inside the docker container,
+# run this to setup dev override and run unit tests.
+make test
+```
+
+### Integration Test
+
+```bash
 # Inside the docker container,
 # run this to setup dev override and run integration tests.
 make test-integration
 ```
 
-
 ### Add a new resource
 
 See [Add a new resource](./add_new_resource.md)