Merge pull request #73 from rajasegar/debugging-docs

[DOCS] Add debugging workflow info docs

Author: Robert Jackson

README.md

@@ -75,6 +75,57 @@ require('codemod-cli').runTransform(
 )
 ```
 
+## Debugging Workflow
+Oftentimes, you want to debug the codemod or the transform to identify issues with the code or to understand
+how the transforms are working, or to troubleshoot why some tests are failing. 
+
+Hence we recommend a debugging work-flow like below to quickly find out what is causing the issue.
+
+### 1. Place `debugger` statements
+Add `debugger` statements, in appropriate places in the code. For example:
+
+```js
+...
+const params = a.value.params.map(p => {
+  debugger;
+  if(p.type === "SubExpression") {
+    return transformNestedSubExpression(p)
+...
+```
+
+### 2. Inspect the process with node debug
+Here we are going to start the tests selectively in node debug mode. Since the
+codemod is bootstrapped using [codemod-cli](https://github.com/rwjblue/codemod-cli) which is using [jest](https://jestjs.io/) in turn
+to run the tests, jest is having an option `-t <name-of-spec>` to run a particular 
+set of tests instead of running the whole test suite.
+
+We are making use of both these features to start our tests in this particular fashion.
+For more details on node debug, visit the [official](https://nodejs.org/en/docs/guides/debugging-getting-started/) 
+Node.js debugging guide, and for jest documentation on tests, [here](https://jestjs.io/docs/en/cli)
+
+```sh
+node --inspect-brk ./node_modules/.bin/codemod-cli -t '<fixture-name>'
+```
+
+For example, if you want to debug the `null-subexp.input.hbs` fixture or only that particular test case is failing
+because of an issue.
+
+```sh
+node --inspect-brk ./node_modules/.bin/codemod-cli -t 'null-subexp'
+```
+
+Sometimes we need to use `--runInBand` flag for the debugger statements to be hit when focusing the test with jest 
+
+For example:
+
+```sh
+node --inspect-brk ./node_modules/.bin/jest --testNamePattern "ember-concurrency transforms correctly" --runInBand
+```
+
+Once you run the above command, your tests will start running in debug mode and your breakpoints will be
+triggered appropriately when that particular block of code gets executed. You can run the debugger inside
+Chrome browser dev-tools. More details on [here](https://developers.google.com/web/tools/chrome-devtools/javascript/)
+
 Contributing
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