diff --git a/source/workbook/tests/test_read.hpp b/source/workbook/tests/test_read.hpp
index 34a0b782..c77bbad7 100644
--- a/source/workbook/tests/test_read.hpp
+++ b/source/workbook/tests/test_read.hpp
@@ -553,4 +553,15 @@ public:
         wb.load(path_helper::get_data_directory("/genuine/empty.xlsx"));
         TS_ASSERT_EQUALS(wb.get_sheet_by_index(0).get_cell("A1").get_value<std::string>(), "This is cell A1 in Sheet 1");
     }
+
+    void test_determine_document_type()
+    {
+        xlnt::workbook wb;
+        TS_ASSERT_THROWS(wb.load(path_helper::get_data_directory("1_empty.txt")), xlnt::invalid_file_error);
+        TS_ASSERT_THROWS(wb.load(path_helper::get_data_directory("2_not-empty.txt")), xlnt::invalid_file_error);
+        TS_ASSERT_THROWS(wb.load(path_helper::get_data_directory("3_empty.zip")), xlnt::invalid_file_error);
+        TS_ASSERT_THROWS(wb.load(path_helper::get_data_directory("4_not-package.zip")), xlnt::invalid_file_error);
+        TS_ASSERT_THROWS(wb.load(path_helper::get_data_directory("5_document.docx")), xlnt::invalid_file_error);
+        TS_ASSERT_THROWS(wb.load(path_helper::get_data_directory("6_presentation.pptx")), xlnt::invalid_file_error);
+    }
 };
diff --git a/source/worksheet/tests/test_worksheet.hpp b/source/worksheet/tests/test_worksheet.hpp
index cb47a2eb..0d456442 100644
--- a/source/worksheet/tests/test_worksheet.hpp
+++ b/source/worksheet/tests/test_worksheet.hpp
@@ -1168,8 +1168,8 @@ public:
             }
         }
 
-        auto const_range = ws_const.get_range("B3:C7");
-        auto const_range_iter = const_range.begin();
+        const auto const_range = ws_const.get_range("B3:C7");
+        auto const_range_iter = const_range.cbegin();
         const_range_iter++;
         const_range_iter--;
         TS_ASSERT_EQUALS(const_range_iter, const_range.begin());
diff --git a/tests/data/1_empty.txt b/tests/data/1_empty.txt
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/data/2_not-empty.txt b/tests/data/2_not-empty.txt
new file mode 100644
index 00000000..041ecf26
--- /dev/null
+++ b/tests/data/2_not-empty.txt
@@ -0,0 +1 @@
+not-empty
diff --git a/tests/data/3_empty.zip b/tests/data/3_empty.zip
new file mode 100644
index 00000000..15cb0ecb
Binary files /dev/null and b/tests/data/3_empty.zip differ
diff --git a/tests/data/4_not-package.zip b/tests/data/4_not-package.zip
new file mode 100644
index 00000000..d80e9910
Binary files /dev/null and b/tests/data/4_not-package.zip differ
diff --git a/tests/data/5_document.docx b/tests/data/5_document.docx
new file mode 100644
index 00000000..2d846668
Binary files /dev/null and b/tests/data/5_document.docx differ
diff --git a/tests/data/6_presentation.pptx b/tests/data/6_presentation.pptx
new file mode 100644
index 00000000..41e8476d
Binary files /dev/null and b/tests/data/6_presentation.pptx differ
diff --git a/tests/data/7_excel-empty.xlsx b/tests/data/7_excel-empty.xlsx
new file mode 100644
index 00000000..1fad86ee
Binary files /dev/null and b/tests/data/7_excel-empty.xlsx differ