Add unit tests for Error class

unitTests/CMakeLists.txt

@@ -6,6 +6,7 @@ add_executable(unit_tests
     test_bmpimage.cpp
     test_cr2header_int.cpp
     test_datasets.cpp
+    test_Error.cpp
     test_DateValue.cpp
     test_enforce.cpp
     test_FileIo.cpp

unitTests/test_Error.cpp

@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <exiv2/error.hpp>
+
+#include <gtest/gtest.h>
+
+using namespace Exiv2;
+
+TEST(Error, parameterInsertion)
+{
+    const Error err_with_3_params(ErrorCode::kerGeneralError, "foo", "bar", "baz");
+    ASSERT_STREQ(err_with_3_params.what(), "Error 1: arg2=bar, arg3=baz, arg1=foo.");
+
+    const Error err_with_no_params(ErrorCode::kerSuccess);
+    ASSERT_STREQ(err_with_no_params.what(), "Success");
+}
+
+TEST(Error, tooManyParameters)
+{
+    const Error err_with_no_params(ErrorCode::kerSuccess, "a param", "another param");
+    ASSERT_STREQ(err_with_no_params.what(), "Success");
+}