harmonize error handling

lib/proformaxml/services/importer.rb

@@ -12,7 +12,7 @@ def initialize(zip:, expected_version: nil)
       @expected_version = expected_version
 
       xml = filestring_from_zip('task.xml')
-      raise PreImportValidationError if xml.nil?
+      raise PreImportValidationError.new(['no task_xml found']) if xml.blank?
 
       @doc = Nokogiri::XML(xml, &:noblanks)
       @task = Task.new
@@ -28,8 +28,7 @@ def proforma_namespace
 
     def perform
       errors = validate
-
-      raise PreImportValidationError.new(errors) if errors.any?
+      raise PreImportValidationError.new(errors.map(&:message)) if errors.any?
 
       @pro_ns = proforma_namespace
       @task_node = @doc.xpath("/#{@pro_ns}:task")

spec/proformaxml/importer_spec.rb

@@ -37,6 +37,17 @@
         expect(importer.instance_variable_get(:@expected_version)).to eql '2.0'
       end
     end
+
+    context 'when zip-file does not contain task.xml' do
+      before do
+        zip_file.write('Foobar')
+        zip_file.rewind
+      end
+
+      it 'raises correct error' do
+        expect { importer }.to raise_error(ProformaXML::PreImportValidationError, /no task_xml found/)
+      end
+    end
   end
 
   describe '#perform' do
@@ -242,7 +253,7 @@
         let(:export_version) { '2.1' }
 
         it 'raises an error' do
-          expect { perform }.to raise_error ProformaXML::PreImportValidationError
+          expect { perform }.to raise_error ProformaXML::PreImportValidationError, /No matching global declaration available for the validation root/
         end
       end
     end