Give more details in tests.md

exercises/shared/.docs/tests.md

@@ -1,3 +1,42 @@
 # Testing on the Command Line
 
-To test your solution to an exercise, open a terminal, go to this exercise's directory, run `roc test <exercise-name>-test.roc`, for example `roc test hello-world-test.roc`, and ensure that all the tests pass.
+To download an exercise, for example `hello-world`, open a terminal and run:
+
+```bash
+exercism download --track roc --exercise hello-world
+```
+
+Then go to the exercise directory and edit the code to solve the exercise. For example:
+
+```bash
+cd {your Exercism folder}/roc/hello-world
+edit HelloWorld.roc
+```
+
+Each exercise comes with a test suite. You can run the tests using the `roc test` command, for example:
+
+```
+roc test hello-world-test.roc
+```
+
+If you've solved the exercise, you should see 0 failed test, for example:
+
+```
+0 failed and 1 passed in 583 ms.
+```
+
+However, if your code has any errors, they will look like this:
+
+```
+── EXPECT FAILED in hello-world-test.roc ───────────────────────────────────────
+
+This expectation failed:
+
+6│  expect hello == "Hello, World!"
+    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+
+1 failed and 0 passed in 1264 ms.
+```
+
+This should help you fix your code. Once your code works, you can submit it using the `exercism submit` command (see `HELP.md` in the exercise directory for more details).