Base: Update js(1) manpage

- Include all options
- Update example REPL session to match current output
- Mention REPL's help()
- Add test mode section

Base/usr/share/man/man1/js.md

@@ -17,11 +17,15 @@ single lines) of code from standard input, evaluates them in one shared
 interpreter context, and prints back their results. This mode is useful for
 quickly experimenting with LibJS.
 
+Run `help()` in REPL mode to see its available built-in functions.
+
 ## Options
 
 * `-A`, `--dump-ast`: Dump the Abstract Syntax Tree after parsing the program.
 * `-l`, `--print-last-result`: Print the result of the last statement executed.
 * `-g`, `--gc-on-every-allocation`: Run garbage collection on every allocation.
+* `-s`, `--syntax-highlight`: Enable live syntax highlighting in the REPL
+* `-t`, `--test-mode`: Run the interpreter with added functionality for the test harness
 
 ## Examples
 
@@ -36,10 +40,33 @@ And here's an example of an interactive REPL session:
 ```js
 $ js
 > function log_sum(a, b) {
-.     console.log(a + b)
-. }
-[object ScriptFunction]
+>     console.log(a + b)
+> }
+undefined
 > log_sum(35, 42)
 77
 undefined
 ```
+
+## Test mode
+
+In test mode, the `load()` function is added to the global object and can be used
+to load further test utility functions defined in `LibJS/Tests/test-common.js`.
+
+Typically a test will look like this:
+
+```js
+load("test-common.js");
+
+try {
+    // test feature
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}
+```
+
+Available functions in `test-common.js`:
+
+* `assert(expression)`: Throws an `AssertionError` if condition does not evaluate to a truthy value
+* `assertNotReached()`: Throws an `AssertionError`, use to ensure certain code paths are never reached