Add TmuxCommandNotFound to tmux_cmd, fix which

- common.which was including environment PATHs, added an kwarg to
  suppress.
- fixed tests to assert unfound path is a None, and tested for
  append_env_path
- fixed test function name to be more appropriate

Author: tony

libtmux/common.py

@@ -150,7 +150,12 @@ class tmux_cmd(object):
     """
 
     def __init__(self, *args, **kwargs):
-        cmd = [which('tmux')]
+
+        tmux_bin = which('tmux')
+        if not tmux_bin:
+            raise(exc.TmuxCommandNotFound)
+
+        cmd = [tmux_bin]
         cmd += args  # add the command arguments to cmd
         cmd = [str(c) for c in cmd]
 
@@ -187,8 +192,10 @@ def __init__(self, *args, **kwargs):
             if not self.stdout:
                 self.stdout = self.stderr[0]
 
-        logger.debug('self.stdout for %s: \n%s' %
-                      (' '.join(cmd), self.stdout))
+        logger.debug(
+            'self.stdout for %s: \n%s' %
+            (' '.join(cmd), self.stdout)
+        )
 
 
 class TmuxMappingObject(collections.MutableMapping):
@@ -329,10 +336,9 @@ def get_by_id(self, id):
         return None
 
 
-def which(exe=None,
-          default_paths=[
-              '/bin', '/sbin', '/usr/bin', '/usr/sbin', '/usr/local/bin']
-          ):
+def which(exe=None, default_paths=[
+            '/bin', '/sbin', '/usr/bin', '/usr/sbin', '/usr/local/bin'
+        ], append_env_path=True):
     """Return path of bin. Python clone of /usr/bin/which.
 
     from salt.util - https://www.github.com/saltstack/salt - license apache
@@ -341,6 +347,8 @@ def which(exe=None,
     :type exe: string
     :param default_path: Application to search PATHs for.
     :type default_path: list
+    :param append_env_path: Append PATHs in environmental variables.
+    :type append_env_path: bool
     :rtype: string
 
     """
@@ -356,8 +364,12 @@ def _is_executable_file_or_link(exe):
     # Enhance POSIX path for the reliability at some environments, when
     # $PATH is changing. This also keeps order, where 'first came, first
     # win' for cases to find optional alternatives
-    search_path = os.environ.get('PATH') and \
-        os.environ['PATH'].split(os.pathsep) or list()
+    if append_env_path:
+        search_path = os.environ.get('PATH') and \
+            os.environ['PATH'].split(os.pathsep) or list()
+    else:
+        search_path = []
+
     for default_path in default_paths:
         if default_path not in search_path:
             search_path.append(default_path)

libtmux/exc.py

@@ -20,6 +20,13 @@ class TmuxSessionExists(LibTmuxException):
     pass
 
 
+class TmuxCommandNotFound(LibTmuxException):
+
+    """Application binary for tmux not found."""
+
+    pass
+
+
 class BadSessionName(LibTmuxException):
 
     """Disallowed session name for tmux (empty, contains periods or colons)."""

tests/test_common.py

@@ -5,7 +5,9 @@
 
 import pytest
 
-from libtmux.common import has_required_tmux_version, which, session_check_name, is_version
+from libtmux.common import (
+    has_required_tmux_version, which, session_check_name, is_version
+)
 from libtmux.exc import LibTmuxException, BadSessionName
 
 version_regex = re.compile(r'([0-9]\.[0-9])|(master)')
@@ -38,10 +40,11 @@ def test_ignores_letter_versions():
     assert result == r'1.8'
 
     # Should not throw
-    assert type(is_version('1.8'))  is bool
+    assert type(is_version('1.8')) is bool
     assert type(is_version('1.8a')) is bool
     assert type(is_version('1.9a')) is bool
 
+
 def test_error_version_less_1_7():
     with pytest.raises(LibTmuxException) as excinfo:
         has_required_tmux_version('1.7')
@@ -55,10 +58,11 @@ def test_error_version_less_1_7():
     has_required_tmux_version('1.9a')
 
 
-def test_which_no_tmuxp_found(monkeypatch):
+def test_which_no_bin_found(monkeypatch):
     monkeypatch.setenv("PATH", "/")
-    which('tmuxp')
-    which('tmuxp', '/')
+    assert which('top')
+    assert which('top', default_paths=['/'])
+    assert not which('top', default_paths=['/'], append_env_path=False)
 
 
 @pytest.mark.parametrize("session_name,raises,exc_msg_regex", [