runcli.py: Fix crash when testing `bst shell` commands

tests/testutils/runcli.py

@@ -5,6 +5,7 @@ import shutil
 import itertools
 import traceback
 import subprocess
+from tempfile import TemporaryFile
 from contextlib import contextmanager, ExitStack
 from ruamel import yaml
 import pytest
@@ -158,28 +159,32 @@ class Cli():
         exception = None
         exit_code = 0
 
-        capture = MultiCapture(out=True, err=True, in_=False, Capture=FDCapture)
-        capture.start_capturing()
+        with TemporaryFile(mode='r') as f:
+            old_stdin = sys.stdin
+            sys.stdin = f
 
-        try:
-            cli.main(args=args or (), prog_name=cli.name, **extra)
-        except SystemExit as e:
-            if e.code != 0:
-                exception = e
+            capture = MultiCapture(out=True, err=True, in_=False, Capture=FDCapture)
+            capture.start_capturing()
 
-            exc_info = sys.exc_info()
-
-            exit_code = e.code
-            if not isinstance(exit_code, int):
-                sys.stdout.write(str(exit_code))
-                sys.stdout.write('\n')
-                exit_code = 1
-        except Exception as e:
-            exception = e
-            exit_code = -1
-            exc_info = sys.exc_info()
-        finally:
-            sys.stdout.flush()
+            try:
+                cli.main(args=args or (), prog_name=cli.name, **extra)
+            except SystemExit as e:
+                if e.code != 0:
+                    exception = e
+
+                exc_info = sys.exc_info()
+
+                exit_code = e.code
+                if not isinstance(exit_code, int):
+                    sys.stdout.write(str(exit_code))
+                    sys.stdout.write('\n')
+                    exit_code = 1
+            except Exception as e:
+                exception = e
+                exit_code = -1
+                exc_info = sys.exc_info()
+            finally:
+                sys.stdout.flush()
 
         out, err = capture.readouterr()
         capture.stop_capturing()