[test] Avoid reusing a.mjs for all js tests. (#7534)

Instead create `<filename>.mjs` named after each test.

Test output now looks like this:

```
$ ./check.py --binaryen-bin=emcc-build/bin binaryenjs_wasm
warning: Binaryen not found (or has not been successfully built to bin/ ?
executing:  /usr/bin/node -e process.stdout.write(typeof WebAssembly)

[ checking binaryen.js testcases (/usr/local/google/home/sbc/dev/wasm/binaryen/emcc-build/bin/binaryen_wasm.js)... ]

executing:  /usr/bin/node atomics.mjs
executing:  /usr/bin/node closed-world.mjs
executing:  /usr/bin/node copy-expression.mjs
executing:  /usr/bin/node custom-section.mjs
...
```

Previously:

```
$ ./check.py --binaryen-bin=emcc-build/bin binaryenjs_wasm
warning: Binaryen not found (or has not been successfully built to bin/ ?
executing:  /usr/bin/node -e process.stdout.write(typeof WebAssembly)

[ checking binaryen.js testcases (/usr/local/google/home/sbc/dev/wasm/binaryen/emcc-build/bin/binaryen_wasm.js)... ]

atomics.js
executing:  /usr/bin/node a.mjs
closed-world.js
executing:  /usr/bin/node a.mjs
copy-expression.js
executing:  /usr/bin/node a.mjs
custom-section.js
executing:  /usr/bin/node a.mjs
debug-info.js
executing:  /usr/bin/node a.mjs
debug-names.js
executing:  /usr/bin/node a.mjs
emit_asmjs.js
...
```

Author: sbc100

scripts/test/binaryenjs.py

@@ -29,19 +29,15 @@ def do_test_binaryen_js_with(which):
 
     print('\n[ checking binaryen.js testcases (' + which + ')... ]\n')
 
-    for s in sorted(os.listdir(os.path.join(shared.options.binaryen_test, 'binaryen.js'))):
-        if not s.endswith('.js'):
-            continue
-        print(s)
-        f = open('a.mjs', 'w')
+    for s in shared.get_tests(shared.get_test_dir('binaryen.js'), ['.js']):
+        basename = os.path.basename(s)
+        outname = os.path.splitext(basename)[0] + '.mjs'
+        f = open(outname, 'w')
         # avoid stdout/stderr ordering issues in some js shells - use just stdout
-        f.write('''
-            console.warn = console.error = console.log;
-        ''')
+        f.write('console.warn = console.error = console.log;')
         binaryen_js = open(which).read()
         f.write(binaryen_js)
-        test_path = os.path.join(shared.options.binaryen_test, 'binaryen.js', s)
-        test_src = open(test_path).read()
+        test_src = open(s).read()
         f.write(support.js_test_wrap().replace('%TEST%', test_src))
         f.close()
 
@@ -57,12 +53,12 @@ def test(cmd):
 
         # run in all possible shells
         if shared.MOZJS:
-            test([shared.MOZJS, '-m', 'a.mjs'])
+            test([shared.MOZJS, '-m', outname])
         if shared.NODEJS:
             if node_has_wasm or 'WebAssembly.' not in test_src:
-                test([shared.NODEJS, 'a.mjs'])
+                test([shared.NODEJS, outname])
             else:
-                print('Skipping ' + test_path + ' because WebAssembly might not be supported')
+                print('Skipping ' + basename + ' because WebAssembly might not be supported')
 
 
 def update_binaryen_js_tests():
@@ -78,12 +74,10 @@ def update_binaryen_js_tests():
     node_has_wasm = shared.NODEJS and support.node_has_webassembly(shared.NODEJS)
     for s in shared.get_tests(shared.get_test_dir('binaryen.js'), ['.js']):
         basename = os.path.basename(s)
-        print(basename)
-        f = open('a.mjs', 'w')
+        outname = os.path.splitext(basename)[0] + '.mjs'
+        f = open(outname, 'w')
         # avoid stdout/stderr ordering issues in some js shells - use just stdout
-        f.write('''
-            console.warn = console.error = console.log;
-        ''')
+        f.write('console.warn = console.error = console.log;')
         f.write(open(shared.BINARYEN_JS).read())
         test_src = open(s).read()
         f.write(support.js_test_wrap().replace('%TEST%', test_src))
@@ -100,9 +94,9 @@ def update(cmd):
 
         # run in available shell
         if shared.MOZJS:
-            update([shared.MOZJS, '-m', 'a.mjs'])
+            update([shared.MOZJS, '-m', outname])
         elif node_has_wasm or 'WebAssembly.' not in test_src:
-            update([shared.NODEJS, 'a.mjs'])
+            update([shared.NODEJS, outname])
         else:
             print('Skipping ' + basename + ' because WebAssembly might not be supported')