Add test helpers

This makes waiting for text robust.

script.addPreloadScript() doesn't export the declared functions, so we
need to attach them to `window`. We also don't need all of them.

bidi.py

@@ -69,6 +69,10 @@ def pick_ports(count: int) -> list[int]:
     return ports
 
 
+def jsquote(js: object) -> str:
+    return json.dumps(js)
+
+
 class WebdriverBidi:
     def __init__(self, headless=False) -> None:
         self.headless = headless
@@ -117,6 +121,9 @@ class WebdriverBidi:
             "log.entryAdded", "browsingContext.domContentLoaded",
         ])
 
+        test_functions = Path("test-functions.js").read_text()
+        await self.bidi("script.addPreloadScript", functionDeclaration=f"() => {{ {test_functions} }}")
+
         # wait for browser to initialize default context
         for _ in range(10):
             realms = (await self.bidi("script.getRealms"))["realms"]
@@ -147,7 +154,11 @@ class WebdriverBidi:
                 if "id" in data and data["id"] in self.pending_commands:
                     log_proto.debug("ws_reader: resolving pending command %i", data["id"])
                     if data["type"] == "success":
-                        self.pending_commands[data["id"]].set_result(data["result"])
+                        result = data["result"]
+                        if result.get("type") == "exception":
+                            self.pending_commands[data["id"]].set_exception(RuntimeError(result["exceptionDetails"]))
+                        else:
+                            self.pending_commands[data["id"]].set_result(result)
                     else:
                         self.pending_commands[data["id"]].set_exception(
                             WebdriverError(f"{data['type']}: {data['message']}"))
@@ -185,8 +196,9 @@ class WebdriverBidi:
         future = asyncio.get_event_loop().create_future()
         self.pending_commands[self.last_id] = future
         self.last_id += 1
-        # we really expect this to be fast, otherwise the browser crashed; in particular, TIMEOUT is too long
-        return await asyncio.wait_for(future, timeout=5)
+        # some calls can take very long (wait for condition);
+        # safe-guard timeout for avoiding eternally hanging tests
+        return await asyncio.wait_for(future, timeout=60)
 
     #
     # BiDi state tracking
@@ -249,6 +261,12 @@ class WebdriverBidi:
         else:
             raise ValueError(f"timed out waiting for {selector}: {last_error}")
 
+    async def wait_js_cond(self, cond: str, error_description: str = "null") -> None:
+        log_command.debug("wait_js_cond(%s)", cond)
+        await self.bidi("script.evaluate",
+                        expression=f"window.ph_wait_cond(() => {cond}, {TIMEOUT * 1000}, {error_description})",
+                        awaitPromise=True, target={"context": self.context})
+
     async def text(self, selector: str) -> str:
         # there is no BiDi way of evaluating a script on a particular element or getting
         # the text of an element, so just use the standard `.textContent` web platform property
@@ -258,6 +276,11 @@ class WebdriverBidi:
                             awaitPromise=False, target={"context": self.context})
         return r['result']['value']
 
+    async def wait_text(self, selector: str, text: str) -> None:
+        await self.wait(selector)
+        await self.wait_js_cond(f"window.ph_text({jsquote(selector)}) === {jsquote(text)}",
+                                error_description=f"() => 'actual text: ' + window.ph_text({jsquote(selector)})")
+
     async def mouse(self, selector: str, button: int = 0, click_count: int = 1) -> None:
         element = await self.locate(selector)
 
@@ -438,19 +461,11 @@ async def main():
 
         print("\n\nSTEP: super-user-indicator")
         try:
-            await d.wait("#super-user-indicator")
+            await d.wait_text("#super-user-indicator", "Limited access")
         except ValueError:
             s = await d.bidi("browsingContext.captureScreenshot", context=d.top_context, origin="document")
             Path("screenshot.png").write_bytes(base64.b64decode(s["data"]))
             raise
-        # FIXME: wait for text helper
-        for _ in range(5):
-            t = await d.text("#super-user-indicator")
-            if t == "Limited access":
-                break
-            await asyncio.sleep(0.5)
-        else:
-            raise ValueError("timed out waiting for #super-user-indicator text")
 
         print("\n\nSTEP: wait/switch frame")
         await d.switch_to_frame('cockpit1:localhost/system')