Fix module class for RPM and Debian distributions #570 (#575)

* Fix module class for RPM and Debian distributions #570

A CentOS system with dpkg package installed fails all packages
is_installed checks. This happens because the decision to use module class
is based on the presence of `dpkg-query` binary.

Co-authored-by: Philippe Pepiot <phil@philpep.org>

Author: guimaluf

test/test_modules.py

@@ -31,6 +31,13 @@
     )
 ])
 
+centos_images = pytest.mark.testinfra_hosts(*[
+    "docker://{}".format(image)
+    for image in (
+        "centos_6", "centos_7",
+    )
+])
+
 
 @all_images
 def test_package(host, docker_image):
@@ -72,6 +79,14 @@ def test_held_package(host):
     assert python.version.startswith("2.7.")
 
 
+@pytest.mark.destructive
+@centos_images
+def test_non_default_package_tool(host):
+    # Make non default pkg tool binary present
+    host.run("install -m a+rx /bin/true /usr/bin/dpkg-query")
+    assert host.package("openssh").is_installed
+
+
 @pytest.mark.destructive
 def test_uninstalled_package_version(host):
     with pytest.raises(AssertionError) as excinfo:

testinfra/modules/package.py

@@ -68,14 +68,22 @@ def get_module_class(cls, host):
             return FreeBSDPackage
         if host.system_info.type in ("openbsd", "netbsd"):
             return OpenBSDPackage
-        if host.exists("dpkg-query"):
+        if host.system_info.distribution in ("debian", "ubuntu"):
             return DebianPackage
-        if host.exists("rpm"):
+        if (
+            host.system_info.distribution
+            and host.system_info.distribution.lower() == "centos"
+        ):
             return RpmPackage
-        if host.exists("apk"):
-            return AlpinePackage
         if host.system_info.distribution == "arch":
             return ArchPackage
+        if host.exists("apk"):
+            return AlpinePackage
+        # Fallback conditions
+        if host.exists("dpkg-query"):
+            return DebianPackage
+        if host.exists("rpm"):
+            return RpmPackage
         raise NotImplementedError