Fix i/o tests using mock (de)compression

Registering (de)compression methods is done with a singleton. But the
tests register them multiple times with different definitions, so we
need to clear the register before every test.

Author: joto

include/osmium/io/compression.hpp

@@ -207,6 +207,10 @@ namespace osmium {
                 return m_callbacks.insert(cc).second;
             }
 
+            void clear_register() {
+                m_callbacks.clear();
+            }
+
             template <typename... TArgs>
             std::unique_ptr<osmium::io::Compressor> create_compressor(const osmium::io::file_compression compression, TArgs&&... args) const {
                 const auto callbacks = find_callbacks(compression);

test/t/io/test_reader_with_mock_decompression.cpp

@@ -80,6 +80,8 @@ TEST_CASE("Test Reader using MockDecompressor") {
 
     std::string fail_in;
 
+    osmium::io::CompressionFactory::instance().clear_register();
+
     osmium::io::CompressionFactory::instance().register_compression(osmium::io::file_compression::gzip,
         [](int /*unused*/, osmium::io::fsync /*unused*/) { return nullptr; },
         [&](int /*unused*/) { return new MockDecompressor(fail_in); },

test/t/io/test_writer_with_mock_compression.cpp

@@ -2,7 +2,6 @@
 
 #include "utils.hpp"
 
-#include <osmium/io/compression.hpp>
 #include <osmium/io/xml_input.hpp>
 #include <osmium/io/xml_output.hpp>
 
@@ -50,6 +49,14 @@ TEST_CASE("Write with mock compressor") {
 
     std::string fail_in;
 
+    osmium::io::CompressionFactory::instance().clear_register();
+
+    osmium::io::CompressionFactory::instance().register_compression(osmium::io::file_compression::none,
+        [](const int /*fd*/, const osmium::io::fsync /*sync*/) { return nullptr; },
+        [](const int fd) { return new osmium::io::NoDecompressor{fd}; },
+        [](const char* buffer, std::size_t size) { return new osmium::io::NoDecompressor{buffer, size}; }
+    );
+
     osmium::io::CompressionFactory::instance().register_compression(osmium::io::file_compression::gzip,
         [&](int /*unused*/, osmium::io::fsync /*unused*/) { return new MockCompressor(fail_in); },
         [](int /*unused*/) { return nullptr; },