Remove duplicate call to shell.main (#687)

* remove duplicate calls to shell.main

* update unit test to count occurrences

* update changes

* update with PR number

CHANGES

@@ -30,6 +30,7 @@ PyVISA Changelog
   Flow control attribute per ivi foundation definition is a flag and
   multiple flow control types can be set.
 - move all setup metadata to pyproject.toml PR #600
+- remove duplicate call to the command loop after running pyvisa-shell PR #687
 
 1.11.3 (07-11-2020)
 -------------------

pyvisa/cmd_line_tools.py

@@ -51,8 +51,6 @@ def visa_main(command: Optional[str] = None) -> None:
         from pyvisa import shell
 
         shell.main("@" + args.backend if args.backend else "")
-
-        shell.main("@" + args.backend if args.backend else "")
     else:
         raise ValueError(
             f"Unknown command {args.command}. Valid values are: info and shell"

pyvisa/testsuite/test_cmd_line_tools.py

@@ -40,4 +40,4 @@ def test_visa_shell(self):
         """Test the visa shell function."""
         with Popen(["pyvisa-shell"], stdin=PIPE, stdout=PIPE) as p:
             stdout, stderr = p.communicate(b"exit")
-        assert b"Welcome to the VISA shell" in stdout
+        assert stdout.count(b"Welcome to the VISA shell") == 1