improve README about testing

README.md

@@ -43,12 +43,30 @@ If you plan to analyze Solidity code you'll also need the [native version of sol
 
 ## Running tests
 
+In order to run tests and coverage reports, you need to run `geth` locally, since some tests depend on it.
+
+Install `geth` from here: <https://github.com/ethereum/go-ethereum/wiki/Building-Ethereum>
+
+Then you can run `geth version` and if you see `Version: 1.8.2-stable` or above, it's OK for testing.
+
+Don't forget to run `geth account new` to generate an account for you if this is the first time you use it.
+
+Then start it like this:
+
+```
+geth --syncmode full --rpc --shh --debug
+```
+
+We use `--syncmode full` here because the `eth.blockNumber` will get increased soon in this mode, which is useful in tests.
+
+If there is no error thrown, you can wait 1 or 2 minutes, then run the tests: 
+
 ```bash
 pip3 install -r requirements.txt
 ./all_tests.sh
 ```
 
-It will run all the tests.
+It may cost you about 3 minutes to run all the tests.
 
 ### Generating test coverage report 
 
@@ -56,7 +74,11 @@ It will run all the tests.
 ./coverage_report.sh
 ```
 
-It will generate a coverage testing report `htmlcov/index.html` in html format, which will be automatically opened in browser.
+It will generate a coverage testing report `coverage_html_report/index.html`, which will be automatically opened in browser. You can find coverage rate and tested/missing code from the report.
+
+Notice there are some tests are running by shell commands(`tests/cmd_line_test.py`), not calling by python, so they are not included in the coverage analysis.
+
+It may cost you about 5 minutes to generate the report.
 
 ## Security analysis