pmbootstrap init: check for required programs (!1845)

Prepare to require "git" in a follow-up patch.

test/test_config_init.py

@@ -0,0 +1,40 @@
+"""
+Copyright 2019 Oliver Smith
+
+This file is part of pmbootstrap.
+
+pmbootstrap is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+pmbootstrap is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with pmbootstrap.  If not, see <http://www.gnu.org/licenses/>.
+"""
+import os
+import pytest
+import sys
+
+# Import from parent directory
+sys.path.insert(0, os.path.realpath(
+    os.path.join(os.path.dirname(__file__) + "/..")))
+import pmb.config.init
+
+
+def test_require_programs(monkeypatch):
+    func = pmb.config.init.require_programs
+
+    # Nothing missing
+    func()
+
+    # Missing program
+    invalid = "invalid-program-name-here-asdf"
+    monkeypatch.setattr(pmb.config, "required_programs", [invalid])
+    with pytest.raises(RuntimeError) as e:
+        func()
+    assert str(e.value).startswith("Can't find all programs")