diff --git a/circle.yml b/circle.yml
index b7a9027ec5..9d05756394 100644
--- a/circle.yml
+++ b/circle.yml
@@ -15,8 +15,6 @@ jobs:
     - run:
         name: "Run codespell"
         command: |
-          sudo pip3 install --upgrade pip setuptools
-          sudo pip3 install codespell
           codespell --quiet-level=4 --ignore-words=./.codespell-whitelist
 
   build: &build
diff --git a/cmake/HunterConfig.cmake b/cmake/HunterConfig.cmake
index 385dd2bbcb..766ba9d818 100644
--- a/cmake/HunterConfig.cmake
+++ b/cmake/HunterConfig.cmake
@@ -1,6 +1,6 @@
 # EVMC: Ethereum Client-VM Connector API.
-# Copyright 2018 The EVMC Authors.
-# Licensed under the Apache License, Version 2.0. See the LICENSE file.
+# Copyright 2019 The EVMC Authors.
+# Licensed under the Apache License, Version 2.0.
 
 # Setup Hunter.
 # Hunter is going to be initialized only if building with tests,
diff --git a/lib/loader/loader.c b/lib/loader/loader.c
index 12b7407b80..c01d337e64 100644
--- a/lib/loader/loader.c
+++ b/lib/loader/loader.c
@@ -1,6 +1,6 @@
 /* EVMC: Ethereum Client-VM Connector API.
- * Copyright 2018 The EVMC Authors.
- * Licensed under the Apache License, Version 2.0. See the LICENSE file.
+ * Copyright 2019 The EVMC Authors.
+ * Licensed under the Apache License, Version 2.0.
  */
 
 #include <evmc/loader.h>
@@ -11,25 +11,29 @@
 #include <stdint.h>
 #include <string.h>
 
-#if _WIN32
+#if defined(EVMC_LOADER_MOCK)
+#include "../../test/unittests/loader_mock.h"
+#elif _WIN32
 #include <Windows.h>
 #define DLL_HANDLE HMODULE
 #define DLL_OPEN(filename) LoadLibrary(filename)
 #define DLL_CLOSE(handle) FreeLibrary(handle)
 #define DLL_GET_CREATE_FN(handle, name) (evmc_create_fn)(uintptr_t) GetProcAddress(handle, name)
-#define HAVE_STRCPY_S 1
 #else
 #include <dlfcn.h>
 #define DLL_HANDLE void*
 #define DLL_OPEN(filename) dlopen(filename, RTLD_LAZY)
 #define DLL_CLOSE(handle) dlclose(handle)
 #define DLL_GET_CREATE_FN(handle, name) (evmc_create_fn)(uintptr_t) dlsym(handle, name)
-#define HAVE_STRCPY_S 0
 #endif
 
 #define PATH_MAX_LENGTH 4096
 
-#if !HAVE_STRCPY_S
+#if !_WIN32
+/*
+ * Provide strcpy_s() for GNU libc.
+ * The availability check might need to adjusted for other C standard library implementations.
+ */
 static void strcpy_s(char* dest, size_t destsz, const char* src)
 {
     size_t len = strlen(src);
diff --git a/test/unittests/CMakeLists.txt b/test/unittests/CMakeLists.txt
index 97fa06fbda..2f7a0b2bf2 100644
--- a/test/unittests/CMakeLists.txt
+++ b/test/unittests/CMakeLists.txt
@@ -1,50 +1,19 @@
 # EVMC: Ethereum Client-VM Connector API.
-# Copyright 2018 The EVMC Authors.
-# Licensed under the Apache License, Version 2.0. See the LICENSE file.
+# Copyright 2019 The EVMC Authors.
+# Licensed under the Apache License, Version 2.0.
 
-add_library(vm-mock SHARED vm_mock.c)
-target_link_libraries(vm-mock PRIVATE evmc)
-
-add_library(vm-mock-default SHARED vm_mock_default.c)
-target_link_libraries(vm-mock-default PRIVATE evmc)
-
-
-if(UNIX)
-    set(cmd create_symlink)
-else()
-    set(cmd copy)
-endif()
-
-add_custom_command(
-    TARGET vm-mock POST_BUILD
-
-    COMMAND ${CMAKE_COMMAND} -E ${cmd} $<TARGET_FILE:vm-mock> libaaa.so
-    COMMAND ${CMAKE_COMMAND} -E ${cmd} $<TARGET_FILE:vm-mock> double_prefix_aaa.evm
-    COMMAND ${CMAKE_COMMAND} -E ${cmd} $<TARGET_FILE:vm-mock> double-prefix-aaa.evm
-    COMMAND ${CMAKE_COMMAND} -E ${cmd} $<TARGET_FILE:vm-mock> eee-bbb.dll
-    COMMAND ${CMAKE_COMMAND} -E ${cmd} $<TARGET_FILE:vm-mock> libeee1.so
-    COMMAND ${CMAKE_COMMAND} -E ${cmd} $<TARGET_FILE:vm-mock> eee2.so
-    COMMAND ${CMAKE_COMMAND} -E ${cmd} $<TARGET_FILE:vm-mock> libeee3.x
-    COMMAND ${CMAKE_COMMAND} -E ${cmd} $<TARGET_FILE:vm-mock> eee4
-    COMMAND ${CMAKE_COMMAND} -E ${cmd} $<TARGET_FILE:vm-mock> _
-    COMMAND ${CMAKE_COMMAND} -E ${cmd} $<TARGET_FILE:vm-mock> lib_.so
-    COMMAND ${CMAKE_COMMAND} -E ${cmd} $<TARGET_FILE:vm-mock> ../aaa.evm
-    COMMAND ${CMAKE_COMMAND} -E ${cmd} $<TARGET_FILE:vm-mock> failure.vm
-    COMMAND ${CMAKE_COMMAND} -E ${cmd} $<TARGET_FILE:vm-mock> abi42.vm
-
-    COMMAND ${CMAKE_COMMAND} -E ${cmd} $<TARGET_FILE:vm-mock-default> default.evmc
-
-    COMMAND ${CMAKE_COMMAND} -E touch empty.file
-)
+add_library(loader-mocked STATIC ${PROJECT_SOURCE_DIR}/lib/loader/loader.c)
+target_link_libraries(loader-mocked PRIVATE evmc)
+target_compile_definitions(loader-mocked PRIVATE EVMC_LOADER_MOCK=1)
 
 add_executable(
     evmc-test
+    loader_mock.h
     test_cpp.cpp
     test_helpers.cpp
     test_instructions.cpp
     test_loader.cpp
 )
 
-target_link_libraries(evmc-test PRIVATE evmc-example-vm instructions loader GTest::gtest GTest::main)
+target_link_libraries(evmc-test PRIVATE loader-mocked evmc-example-vm instructions GTest::gtest GTest::main)
 set_target_properties(evmc-test PROPERTIES RUNTIME_OUTPUT_DIRECTORY ..)
-add_dependencies(evmc-test vm-mock)
diff --git a/test/unittests/loader_mock.h b/test/unittests/loader_mock.h
new file mode 100644
index 0000000000..a012c8ff8d
--- /dev/null
+++ b/test/unittests/loader_mock.h
@@ -0,0 +1,42 @@
+/* EVMC: Ethereum Client-VM Connector API.
+ * Copyright 2019 The EVMC Authors.
+ * Licensed under the Apache License, Version 2.0.
+ */
+
+/**
+ * @file
+ * The loader OS mock for opening DLLs. To be inserted in loader.c for unit tests.
+ */
+
+static const int magic_handle = 0xE7AC;
+
+const char* evmc_test_library_path = NULL;
+const char* evmc_test_library_symbol = NULL;
+evmc_create_fn evmc_test_create_fn = NULL;
+
+static int evmc_test_load_library(const char* filename)
+{
+    if (filename && evmc_test_library_path && strcmp(filename, evmc_test_library_path) == 0)
+        return magic_handle;
+    return 0;
+}
+
+static void evmc_test_free_library(int handle)
+{
+    (void)handle;
+}
+
+static evmc_create_fn evmc_test_get_symbol_address(int handle, const char* symbol)
+{
+    if (handle != magic_handle)
+        return NULL;
+
+    if (evmc_test_library_symbol && strcmp(symbol, evmc_test_library_symbol) == 0)
+        return evmc_test_create_fn;
+    return NULL;
+}
+
+#define DLL_HANDLE int
+#define DLL_OPEN(filename) evmc_test_load_library(filename)
+#define DLL_CLOSE(handle) evmc_test_free_library(handle)
+#define DLL_GET_CREATE_FN(handle, name) evmc_test_get_symbol_address(handle, name)
diff --git a/test/unittests/test_loader.cpp b/test/unittests/test_loader.cpp
index 3a3b332a53..38e34405c3 100644
--- a/test/unittests/test_loader.cpp
+++ b/test/unittests/test_loader.cpp
@@ -1,6 +1,6 @@
 // EVMC: Ethereum Client-VM Connector API.
-// Copyright 2018 The EVMC Authors.
-// Licensed under the Apache License, Version 2.0. See the LICENSE file.
+// Copyright 2019 The EVMC Authors.
+// Licensed under the Apache License, Version 2.0.
 
 #include <evmc/loader.h>
 
@@ -14,126 +14,115 @@ static constexpr bool is_windows = true;
 static constexpr bool is_windows = false;
 #endif
 
-TEST(loader, nonexistent)
+extern "C" {
+extern const char* evmc_test_library_path;
+extern const char* evmc_test_library_symbol;
+extern evmc_create_fn evmc_test_create_fn;
+}
+
+class loader : public ::testing::Test
 {
-    evmc_loader_error_code ec;
-    auto x = evmc_load("nonexistent", &ec);
-    EXPECT_EQ(ec, EVMC_LOADER_CANNOT_OPEN);
-    EXPECT_EQ(x, nullptr);
+protected:
+    void setup(const char* path, const char* symbol, evmc_create_fn fn) noexcept
+    {
+        evmc_test_library_path = path;
+        evmc_test_library_symbol = symbol;
+        evmc_test_create_fn = fn;
+    }
+};
 
-    x = evmc_load("nonexistent", nullptr);
-    EXPECT_EQ(x, nullptr);
+static evmc_instance* create_aaa()
+{
+    return (evmc_instance*)0xaaa;
 }
 
-TEST(loader, longpath)
+static evmc_instance* create_eee_bbb()
 {
-    std::vector<char> path(5000, 'a');
-    *path.rbegin() = 0;
-
-    evmc_loader_error_code ec;
-    auto x = evmc_load(path.data(), &ec);
-    EXPECT_EQ(ec, EVMC_LOADER_INVALID_ARGUMENT);
-    EXPECT_EQ(x, nullptr);
+    return (evmc_instance*)0xeeebbb;
+}
 
-    x = evmc_load(path.data(), nullptr);
-    EXPECT_EQ(x, nullptr);
+static evmc_instance* create_failure()
+{
+    return nullptr;
 }
 
-TEST(loader, not_so)
+static evmc_instance* create_abi42()
 {
-    auto path = "unittests/empty.file";
+    static int abi_version = 42;
+    return reinterpret_cast<evmc_instance*>(&abi_version);
+}
 
+TEST_F(loader, load_nonexistent)
+{
+    constexpr auto path = "nonexistent";
     evmc_loader_error_code ec;
-    auto x = evmc_load(path, &ec);
+    EXPECT_EQ(evmc_load(path, &ec), nullptr);
     EXPECT_EQ(ec, EVMC_LOADER_CANNOT_OPEN);
-    EXPECT_EQ(x, nullptr);
-
-    x = evmc_load(path, nullptr);
-    EXPECT_EQ(x, nullptr);
+    EXPECT_EQ(evmc_load(path, nullptr), nullptr);
 }
 
-TEST(loader, null_path)
+TEST_F(loader, load_long_path)
 {
+    const std::string path(5000, 'a');
     evmc_loader_error_code ec;
-    auto x = evmc_load(nullptr, &ec);
+    EXPECT_EQ(evmc_load(path.c_str(), &ec), nullptr);
     EXPECT_EQ(ec, EVMC_LOADER_INVALID_ARGUMENT);
-    EXPECT_EQ(x, nullptr);
-
-    x = evmc_load(nullptr, nullptr);
-    EXPECT_EQ(x, nullptr);
+    EXPECT_EQ(evmc_load(path.c_str(), nullptr), nullptr);
 }
 
-TEST(loader, empty_path)
+TEST_F(loader, load_null_path)
 {
     evmc_loader_error_code ec;
-    auto x = evmc_load("", &ec);
+    EXPECT_EQ(evmc_load(nullptr, &ec), nullptr);
     EXPECT_EQ(ec, EVMC_LOADER_INVALID_ARGUMENT);
-    EXPECT_EQ(x, nullptr);
-
-    x = evmc_load("", nullptr);
-    EXPECT_EQ(x, nullptr);
+    EXPECT_EQ(evmc_load(nullptr, nullptr), nullptr);
 }
 
-TEST(loader, aaa)
+TEST_F(loader, load_empty_path)
 {
-    auto path = "unittests/libaaa.so";
-
     evmc_loader_error_code ec;
-    auto fn = evmc_load(path, &ec);
-    ASSERT_NE(fn, nullptr);
-    EXPECT_EQ(ec, EVMC_LOADER_SUCCESS);
-    EXPECT_EQ((uintptr_t)fn(), 0xaaa);
-
-    fn = evmc_load(path, nullptr);
-    ASSERT_NE(fn, nullptr);
-    EXPECT_EQ((uintptr_t)fn(), 0xaaa);
+    EXPECT_EQ(evmc_load("", &ec), nullptr);
+    EXPECT_EQ(ec, EVMC_LOADER_INVALID_ARGUMENT);
+    EXPECT_EQ(evmc_load("", nullptr), nullptr);
 }
 
-TEST(loader, prefix_aaa)
+TEST_F(loader, load_prefix_aaa)
 {
-    auto paths = {"unittests/double-prefix-aaa.evm", "unittests/double_prefix_aaa.evm"};
+    auto paths = {
+        "./aaa.evm",
+        "aaa.evm",
+        "unittests/libaaa.so",
+        "unittests/double-prefix-aaa.evm",
+        "unittests/double_prefix_aaa.evm",
+    };
 
     for (auto& path : paths)
     {
+        setup(path, "evmc_create_aaa", create_aaa);
         evmc_loader_error_code ec;
         auto fn = evmc_load(path, &ec);
-        ASSERT_NE(fn, nullptr);
         EXPECT_EQ(ec, EVMC_LOADER_SUCCESS);
+        ASSERT_NE(fn, nullptr);
         EXPECT_EQ((uintptr_t)fn(), 0xaaa);
     }
 }
 
-TEST(loader, eee_bbb)
+TEST_F(loader, load_eee_bbb)
 {
-    auto path = "unittests/eee-bbb.dll";
-
+    setup("unittests/eee-bbb.dll", "evmc_create_eee_bbb", create_eee_bbb);
     evmc_loader_error_code ec;
-    auto fn = evmc_load(path, &ec);
+    auto fn = evmc_load(evmc_test_library_path, &ec);
     ASSERT_NE(fn, nullptr);
     EXPECT_EQ(ec, EVMC_LOADER_SUCCESS);
     EXPECT_EQ((uintptr_t)fn(), 0xeeebbb);
 }
 
-#if _WIN32
-TEST(loader, nextto)
-{
-    // On Unix dlopen searches for system libs when the path does not contain "/".
-
-    auto path = "aaa.evm";
 
-    evmc_loader_error_code ec;
-    auto fn = evmc_load(path, &ec);
-    ASSERT_NE(fn, nullptr);
-    EXPECT_EQ(ec, EVMC_LOADER_SUCCESS);
-    EXPECT_EQ((uintptr_t)fn(), 0xaaa);
-}
-#endif
-
-TEST(loader, windows_path)
+TEST_F(loader, load_windows_path)
 {
     auto paths = {
-        "./aaa.evm",
-        ".\\aaa.evm",
+        "./eee-bbb.evm",
+        ".\\eee-bbb.evm",
         "./unittests/eee-bbb.dll",
         "./unittests\\eee-bbb.dll",
         ".\\unittests\\eee-bbb.dll",
@@ -143,133 +132,59 @@ TEST(loader, windows_path)
 
     for (auto& path : paths)
     {
-        bool is_windows_path = std::strchr(path, '\\') != nullptr;
+        bool should_open = is_windows || std::strchr(path, '\\') == nullptr;
+        setup(should_open ? path : nullptr, "evmc_create_eee_bbb", create_eee_bbb);
 
-        if (is_windows_path && !is_windows)
-        {
-            evmc_loader_error_code ec;
-            auto fn = evmc_load(path, &ec);
-            EXPECT_EQ(fn, nullptr);
-            EXPECT_EQ(ec, EVMC_LOADER_CANNOT_OPEN);
-        }
-        else
-        {
-            evmc_loader_error_code ec;
-            auto fn = evmc_load(path, &ec);
-            EXPECT_NE(fn, nullptr);
-            EXPECT_EQ(ec, EVMC_LOADER_SUCCESS);
-        }
+        evmc_loader_error_code ec;
+        evmc_load(path, &ec);
+        EXPECT_EQ(ec, should_open ? EVMC_LOADER_SUCCESS : EVMC_LOADER_CANNOT_OPEN);
     }
 }
 
-TEST(loader, eee1)
-{
-    auto path = "unittests/libeee1.so";
-
-    evmc_loader_error_code ec;
-    auto x = evmc_load(path, &ec);
-    EXPECT_EQ(ec, EVMC_LOADER_SYMBOL_NOT_FOUND);
-    EXPECT_EQ(x, nullptr);
-
-    x = evmc_load(path, nullptr);
-    EXPECT_EQ(x, nullptr);
-}
-
-TEST(loader, eee2)
-{
-    auto path = "unittests/eee2.so";
-
-    evmc_loader_error_code ec;
-    auto x = evmc_load(path, &ec);
-    EXPECT_EQ(ec, EVMC_LOADER_SYMBOL_NOT_FOUND);
-    EXPECT_EQ(x, nullptr);
-
-    x = evmc_load(path, nullptr);
-    EXPECT_EQ(x, nullptr);
-}
-
-TEST(loader, eee3)
-{
-    auto path = "unittests/libeee3.x";
-
-    evmc_loader_error_code ec;
-    auto x = evmc_load(path, &ec);
-    EXPECT_EQ(ec, EVMC_LOADER_SYMBOL_NOT_FOUND);
-    EXPECT_EQ(x, nullptr);
-
-    x = evmc_load(path, nullptr);
-    EXPECT_EQ(x, nullptr);
-}
-
-#if !_WIN32
-TEST(loader, eee4)
+TEST_F(loader, load_symbol_not_found)
 {
-    // Windows is not loading DLLs without extensions.
-    auto path = "unittests/eee4";
+    auto paths = {"libaaa1.so", "eee2.so", "libeee3.x", "eee4", "_", "lib_.so"};
 
-    evmc_loader_error_code ec;
-    auto x = evmc_load(path, &ec);
-    EXPECT_EQ(ec, EVMC_LOADER_SYMBOL_NOT_FOUND);
-    EXPECT_EQ(x, nullptr);
-
-    x = evmc_load(path, nullptr);
-    EXPECT_EQ(x, nullptr);
-}
-
-TEST(loader, _)
-{
-    // Windows is not loading DLLs without extensions.
-    auto path = "unittests/_";
-
-    evmc_loader_error_code ec;
-    auto x = evmc_load(path, &ec);
-    EXPECT_EQ(ec, EVMC_LOADER_SYMBOL_NOT_FOUND);
-    EXPECT_EQ(x, nullptr);
-
-    x = evmc_load(path, nullptr);
-    EXPECT_EQ(x, nullptr);
-}
-#endif
-
-TEST(loader, lib_)
-{
-    // Windows is not loading DLLs without extensions.
-    auto path = "unittests/lib_.so";
-
-    evmc_loader_error_code ec;
-    auto x = evmc_load(path, &ec);
-    EXPECT_EQ(ec, EVMC_LOADER_SYMBOL_NOT_FOUND);
-    EXPECT_EQ(x, nullptr);
+    for (auto& path : paths)
+    {
+        setup(path, "evmc_create_aaa", create_aaa);
 
-    x = evmc_load(path, nullptr);
-    EXPECT_EQ(x, nullptr);
+        evmc_loader_error_code ec;
+        EXPECT_EQ(evmc_load(evmc_test_library_path, &ec), nullptr);
+        EXPECT_EQ(ec, EVMC_LOADER_SYMBOL_NOT_FOUND);
+        EXPECT_EQ(evmc_load(evmc_test_library_path, nullptr), nullptr);
+    }
 }
 
-TEST(loader, load_default)
+TEST_F(loader, load_default_symbol)
 {
-    auto path = "unittests/default.evmc";
+    setup("default.evmc", "evmc_create", create_aaa);
 
     evmc_loader_error_code ec;
-    auto fn = evmc_load(path, &ec);
+    auto fn = evmc_load(evmc_test_library_path, &ec);
     EXPECT_EQ(ec, EVMC_LOADER_SUCCESS);
-    EXPECT_EQ((uintptr_t)fn(), 0xdeaf);
+    EXPECT_EQ(fn, &create_aaa);
 
-    fn = evmc_load(path, nullptr);
-    EXPECT_EQ((uintptr_t)fn(), 0xdeaf);
+    fn = evmc_load(evmc_test_library_path, nullptr);
+    EXPECT_EQ(fn, &create_aaa);
 }
 
-TEST(loader, load_and_create_failure)
+TEST_F(loader, load_and_create_failure)
 {
+    setup("failure.vm", "evmc_create", create_failure);
+
     evmc_loader_error_code ec;
-    auto vm = evmc_load_and_create("unittests/failure.vm", &ec);
+    auto vm = evmc_load_and_create(evmc_test_library_path, &ec);
     EXPECT_EQ(vm, nullptr);
     EXPECT_EQ(ec, EVMC_LOADER_INSTANCE_CREATION_FAILURE);
 }
 
-TEST(loader, load_and_create_abi_mismatch)
+TEST_F(loader, load_and_create_abi_mismatch)
 {
+    setup("abi42.vm", "evmc_create", create_abi42);
+
     evmc_loader_error_code ec;
-    auto vm = evmc_load_and_create("unittests/abi42.vm", &ec);
+    auto vm = evmc_load_and_create(evmc_test_library_path, &ec);
     EXPECT_EQ(vm, nullptr);
     EXPECT_EQ(ec, EVMC_LOADER_ABI_VERSION_MISMATCH);
 }
diff --git a/test/unittests/vm_mock.c b/test/unittests/vm_mock.c
deleted file mode 100644
index 650d97f8b8..0000000000
--- a/test/unittests/vm_mock.c
+++ /dev/null
@@ -1,30 +0,0 @@
-/* EVMC: Ethereum Client-VM Connector API.
- * Copyright 2018 The EVMC Authors.
- * Licensed under the Apache License, Version 2.0. See the LICENSE file.
- */
-
-#include <evmc/evmc.h>
-#include <evmc/utils.h>
-
-EVMC_EXPORT void* evmc_create_aaa()
-{
-    return (void*)0xaaa;
-}
-
-EVMC_EXPORT void* evmc_create_eee_bbb()
-{
-    return (void*)0xeeebbb;
-}
-
-EVMC_EXPORT void* evmc_create_failure()
-{
-    return NULL;
-}
-
-EVMC_EXPORT struct evmc_instance* evmc_create_abi42()
-{
-    static struct evmc_instance instance = {
-        .abi_version = 42,
-    };
-    return &instance;
-}
diff --git a/test/unittests/vm_mock_default.c b/test/unittests/vm_mock_default.c
deleted file mode 100644
index d063a365c1..0000000000
--- a/test/unittests/vm_mock_default.c
+++ /dev/null
@@ -1,11 +0,0 @@
-/* EVMC: Ethereum Client-VM Connector API.
- * Copyright 2018 The EVMC Authors.
- * Licensed under the Apache License, Version 2.0. See the LICENSE file.
- */
-
-#include <evmc/utils.h>
-
-EVMC_EXPORT void* evmc_create()
-{
-    return (void*)0xdeaf;
-}