diff --git a/js/ReadMe.md b/js/ReadMe.md
index 037d5b6723d..efa62efcc7f 100644
--- a/js/ReadMe.md
+++ b/js/ReadMe.md
@@ -25,3 +25,45 @@ We love contributions! The JavaScript translation could really use your help! If
 
 * check the [contributing section](https://github.com/JetBrains/kotlin/blob/master/ReadMe.md) on general stuff like getting the code etc
 * try fix one of the pending [JavaScript translation issues](https://youtrack.jetbrains.com/issues/KT?q=Subsystems:%20%7BBackend.%20JS%7D%20-Resolved)
+
+## Testing the Kotlin/JS compiler
+
+The following Gradle tasks are responsible for testing the Kotlin/JS compiler:
+- `:js:js.tests:jsIrTest` — run JS tests against the IR backend, plus the same tests with dead code elimination (DCE) enabled.
+- `:js:js.tests:jsTest` — run JS tests against the legacy backend, plus the same tests with DCE enabled.
+- `:js:js.tests:quickTest` — run JS tests against the legacy backend. No DCE.
+- `:js:js.tests:test` — run all JS tests, against both the legacy and the IR backends, plus the same tests with DCE enabled.
+
+The JavaScript files generated from the test files are located in the following directories, divided by the translation mode:
+- `js/js.tests/build/out` — JS files generated with the `FULL` translation mode (all modules are compiled into one big JS file)
+- `js/js.tests/build/out-min` — the same as previous, but with DCE applied.
+- `js/js.tests/build/out-per-module` — JS files generated with the `PER_MODULE` translation mode (each module is compiled into a separate JS file)
+- `js/js.tests/build/out-per-module-min` — the same as previous, but with DCE applied. 
+
+There are multiple kinds of tests. Here are some of them:
+
+- Box tests. Those are the tests that we are often most interested in, they are located in `js/js.translator/testData/box`.
+Such tests must contain a `fn box(): String` function. If this function returns `"OK"`,
+the test is considered passed, and if it returns anything else, the test is considered failed.
+- Line number tests, located in `js/js.translator/testData/lineNumbers`. These are to ensure that the debug info in the generated JavaScript matches some expectation.
+The expectation is written in a comment staring with `// LINES(JS):` or `// LINES(JS_IR):`.
+These comments contain a list of line numbers in the test file that the compiler output is generated from.
+The actual line numbers can be viewed in the generated JS file whose name ends with `-lines.js`.
+- TypeScript export tests, located in `js/js.translator/testData/typescript-export`.
+These test that the generated `.d.ts` (TypeScript definitions) file matches the reference `.d.ts` file.
+- Also, some tests located in `compiler/testData/codegen` are shared between the JS and the JVM backends.
+
+### Manually running the generated JS files (IR backend only)
+There is a helpful tool for running and debugging JS code generated from test files right in Intellij IDEA.
+
+Note that this will only work for files generated with the IR backend in the `FULL` translation mode,
+because these files are self-sufficient and don't require any dependencies.
+
+Just open a generated JS file located in `js/js.tests/build/out`, select
+the "run IR test in node.js" run configuration in IDEA, and click on the "Run" or "Debug" icon.
+The test output will be printed in the console.
+
+Bonus: debugging is supported! You can set a breakpoint in a test file, open the generated JS file,
+select the "run IR test in node.js" run configuration and click on the "Debug" icon.
+The execution should pause and the breakpoint will be hit.
+This works because a source map located next to the generated JS file.