tests: fix clipboard test

First of all, wait for the zenity process to finish, do not leak it.

But then, adjust the test string to not be a single long line - zenity
often hangs on a single 300k line.

Fixes QubesOS/qubes-issues#9646

qubes/tests/integ/basic.py

@@ -619,7 +619,7 @@ async def _test_clipboard(
         p = await testvm1.run("cat > /tmp/source.txt", stdin=subprocess.PIPE)
         await p.communicate(test_string.encode())
         window_title = "user@{}".format(testvm1.name)
-        await testvm1.run(
+        p = await testvm1.run(
             "zenity --text-info "
             "--filename=/tmp/source.txt "
             "--editable "
@@ -639,7 +639,13 @@ async def _test_clipboard(
         await asyncio.sleep(5)
         subprocess.check_call(["xdotool", "key", "ctrl+shift+c", "Escape"])
 
-        await self.wait_for_window_coro(window_title, show=False)
+        try:
+            await asyncio.wait_for(p.communicate(), 5)
+        except asyncio.TimeoutError:
+            # this kills only the qrexec-client process, not zenity itself,
+            # but it's good enough for the test
+            p.terminate()
+            await p.wait()
 
         clipboard_content = (
             open("/var/run/qubes/qubes-clipboard.bin", "r").read().strip()
@@ -718,14 +724,14 @@ def test_000_clipboard(self):
         spawn.find_executable("xdotool"), "xdotool not installed"
     )
     def test_001_clipboard_64k(self):
-        test_string = "test123abc" * 6400
+        test_string = "test123ab\n" * 6400
         self.loop.run_until_complete(self._test_clipboard(test_string))
 
     @unittest.skipUnless(
         spawn.find_executable("xdotool"), "xdotool not installed"
     )
     def test_002_clipboard_200k_truncated(self):
-        test_string = "test123abc" * 20000
+        test_string = "test123ab\n" * 20000
         self.loop.run_until_complete(
             self._test_clipboard(
                 test_string, expect_content="", expect_source_name=""
@@ -736,7 +742,7 @@ def test_002_clipboard_200k_truncated(self):
         spawn.find_executable("xdotool"), "xdotool not installed"
     )
     def test_002_clipboard_200k(self):
-        test_string = "test123abc" * 20000
+        test_string = "test123ab\n" * 20000
         self.loop.run_until_complete(
             self._test_clipboard(
                 test_string, set_features={"gui-max-clipboard-size": 200_000}
@@ -747,7 +753,7 @@ def test_002_clipboard_200k(self):
         spawn.find_executable("xdotool"), "xdotool not installed"
     )
     def test_002_clipboard_300k(self):
-        test_string = "test123abc" * 30000
+        test_string = "test123ab\n" * 30000
         self.loop.run_until_complete(
             self._test_clipboard(
                 test_string,