tests: Add unit test coverage for #539

Signed-off-by: Cole Robinson <crobinso@redhat.com>

tests/data/xmlparse/emulator-custom.xml

@@ -0,0 +1,22 @@
+<domain type='kvm'>
+  <name>manual-emulator-test</name>
+  <metadata>
+    <libosinfo:libosinfo xmlns:libosinfo="http://libosinfo.org/xmlns/libvirt/domain/1.0">
+      <libosinfo:os id="http://fedoraproject.org/fedora/unknown"/>
+    </libosinfo:libosinfo>
+  </metadata>
+  <memory unit='KiB'>8388608</memory>
+  <currentMemory unit='KiB'>8388608</currentMemory>
+  <vcpu placement='static'>8</vcpu>
+  <os>
+    <type arch='mips' machine='some-unknown-machine'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/my/manual/emulator</emulator>
+  </devices>
+</domain>
+

tests/test_xmlparse.py

@@ -1170,3 +1170,34 @@ def testDiskSourceAbspath():
     # ...unless it's a URL
     disk.set_source_path("http://example.com/foobar3")
     assert disk.get_source_path() == "http://example.com/foobar3"
+
+
+def testUnknownEmulatorDomcapsLookup(monkeypatch):
+    """
+    Libvirt can handle defining a VM with a custom emulator, one not detected
+    by `virsh capabilities`. An appropriate `virsh domcapabilities` call will
+    inspect the emulator and return relevant info.
+
+    This test ensures that for parsing XML the `virsh capabilities` failure
+    isn't fatal, and we attempt to return valid `virsh domcapabilities` data
+    """
+
+    seen = False
+    def fake_build_from_params(conn, emulator, arch, machine, hvtype):
+        nonlocal seen
+        seen = True
+        assert arch == "mips"
+        assert machine == "some-unknown-machine"
+        assert emulator == "/my/manual/emulator"
+        return virtinst.DomainCapabilities(conn)
+
+    monkeypatch.setattr(
+        "virtinst.DomainCapabilities.build_from_params",
+        fake_build_from_params)
+
+    conn = utils.URIs.open_kvm()
+    xml = open(DATADIR + "emulator-custom.xml").read()
+    guest = virtinst.Guest(conn, xml)
+    assert guest.lookup_domcaps()
+    assert guest.lookup_domcaps()
+    assert seen