Fix fallback prompt & improve info on test failure

IPython/core/tests/test_shellapp.py

@@ -52,5 +52,9 b' class TestFileToRun(unittest.TestCase, tt.TempFileMixin):'
         self.mktmp(src)
 
         out, err = tt.ipexec(self.fname, options=['-i'],
-                           commands=['"__file__" in globals()', 'exit()'])
-        self.assertIn("False", out)
+                           commands=['"__file__" in globals()', 'print(123)', 'exit()'])
+        if 'False' not in out:
+            print("Subprocess stderr:")
+            print(err)
+            print('-----')
+            raise AssertionError("'False' not found in %r" % out)

IPython/terminal/interactiveshell.py

@@ -229,16 +229,15 b' class TerminalInteractiveShell(InteractiveShell):'
     def init_prompt_toolkit_cli(self):
         if self.simple_prompt:
             # Fall back to plain non-interactive output for tests.
-            # This is very limited, and only accepts a single line.
+            # This is very limited.
             def prompt():
-                isp = self.input_splitter
+                itm = self.input_transformer_manager
                 prompt_text = "".join(x[1] for x in self.prompts.in_prompt_tokens())
+                lines = [input(prompt_text)]
                 prompt_continuation = "".join(x[1] for x in self.prompts.continuation_prompt_tokens())
-                while isp.push_accepts_more():
-                    line = input(prompt_text)
-                    isp.push(line)
-                    prompt_text = prompt_continuation
-                return isp.source_reset()
+                while not itm.check_complete('\n'.join(lines)):
+                    lines.append( input(prompt_continuation) )
+                return '\n'.join(lines)
             self.prompt_for_code = prompt
             return