App: Improve Metadata error handling

Report XML parse exception details.

src/Mod/Test/CMakeLists.txt

@@ -18,6 +18,9 @@ SET(Test_SRCS
 
 SET(TestData_SRCS
     TestData/basic_metadata.xml
+    TestData/bad_root_node.xml
+    TestData/bad_xml.xml
+    TestData/bad_version.xml
 )
 
 SOURCE_GROUP("" FILES ${Test_SRCS} ${TestData_SRCS})

src/Mod/Test/Metadata.py

@@ -31,6 +31,40 @@ class TestMetadata(unittest.TestCase):
     def setUp(self):
         self.test_dir = os.path.join(FreeCAD.getHomePath(), "Mod", "Test", "TestData")
 
+    def test_xml_constructor(self):
+        try:
+            filename = os.path.join(self.test_dir, "basic_metadata.xml")
+            md = FreeCAD.Metadata(filename)
+        except Exception:
+            self.fail("Metadata construction from XML file failed")
+
+        try:
+            filename = os.path.join(self.test_dir, "bad_root_node.xml")
+            md = FreeCAD.Metadata(filename)
+        except Exception as e:
+            FreeCAD.Console.PrintMessage(str(e) + "\n")
+            pass
+        else:
+            self.fail("Metadata construction from XML file with bad root node did not raise an exception")
+
+        try:
+            filename = os.path.join(self.test_dir, "bad_xml.xml")
+            md = FreeCAD.Metadata(filename)
+        except Exception as e:
+            FreeCAD.Console.PrintMessage(str(e) + "\n")
+            pass
+        else:
+            self.fail("Metadata construction from invalid XML file did not raise an exception")
+
+        try:
+            filename = os.path.join(self.test_dir, "bad_version.xml")
+            md = FreeCAD.Metadata(filename)
+        except Exception as e:
+            FreeCAD.Console.PrintMessage(str(e) + "\n")
+            pass
+        else:
+            self.fail("Metadata construction from XML file with bad version did not raise an exception")
+
     def test_toplevel_tags(self):
         filename = os.path.join(self.test_dir, "basic_metadata.xml")
         md = FreeCAD.Metadata(filename)

src/Mod/Test/TestData/bad_root_node.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8" standalone="no" ?>
+<notpackage format="1" xmlns="https://wiki.freecad.org/Package_Metadata">
+  <name>Bad root node</name>
+  <description>The root node is not called "package".</description>
+  <version>1.0.0</version>
+</notpackage>

src/Mod/Test/TestData/bad_version.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8" standalone="no" ?>
+<package format="2" xmlns="https://wiki.freecad.org/Package_Metadata">
+	<name>Bad format</name>
+	<description>There is no such thing as format version 2 (yet).</description>
+	<version>1.0.0</version>
+</package>

src/Mod/Test/TestData/bad_xml.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8" standalone="no" ?>
+<package format="1" xmlns="https://wiki.freecad.org/Package_Metadata">
+  <name>Bad XML</notname>
+  <description>The name tag is not closed properly.</description>
+</package>