diff --git a/test/test_asserts.cpp b/test/test_asserts.cpp
index 5721ee9..01a34cb 100644
--- a/test/test_asserts.cpp
+++ b/test/test_asserts.cpp
@@ -69,6 +69,26 @@ TEST(test_asserts, check_does_not_throw_if_condition_is_true) {
   EXPECT_NO_THROW(rcpputils::check_true(true));
 }
 
+TEST(test_asserts, assertion_exception_what_message) {
+  const rcpputils::AssertionException ex("assertion failed");
+  EXPECT_STREQ("assertion failed", ex.what());
+}
+
+TEST(test_asserts, illegal_state_exception_what_message) {
+  const rcpputils::IllegalStateException ex("illegal state");
+  EXPECT_STREQ("illegal state", ex.what());
+}
+
+TEST(test_asserts, assertion_exception_empty_message) {
+  const rcpputils::AssertionException ex("");
+  EXPECT_STREQ("", ex.what());
+}
+
+TEST(test_asserts, illegal_state_exception_empty_message) {
+  const rcpputils::IllegalStateException ex("");
+  EXPECT_STREQ("", ex.what());
+}
+
 #ifndef NDEBUG
 TEST(test_asserts, assert_true_throws_if_condition_is_false_and_ndebug_not_set) {
   EXPECT_THROW(rcpputils::assert_true(false), rcpputils::AssertionException);
diff --git a/test/test_env.cpp b/test/test_env.cpp
index 81ca59c..b86dcd1 100644
--- a/test/test_env.cpp
+++ b/test/test_env.cpp
@@ -80,3 +80,11 @@ TEST(TestSetEnv, test_set_env) {
     "",
     rcpputils::get_env_var("NEW_ENV_VAR").c_str());
 }
+
+TEST(TestSetEnv, test_set_env_empty_value) {
+  // Setting to empty string is distinct from unsetting.
+  EXPECT_TRUE(rcpputils::set_env_var("EMPTY_VALUE_VAR", ""));
+  EXPECT_STREQ("", rcpputils::get_env_var("EMPTY_VALUE_VAR").c_str());
+  // Cleanup
+  EXPECT_TRUE(rcpputils::set_env_var("EMPTY_VALUE_VAR", nullptr));
+}
diff --git a/test/test_filesystem_helper.cpp b/test/test_filesystem_helper.cpp
index 01bcfb2..793b75d 100644
--- a/test/test_filesystem_helper.cpp
+++ b/test/test_filesystem_helper.cpp
@@ -16,6 +16,7 @@
 
 #include <fstream>
 #include <string>
+#include <vector>
 
 #include "rcpputils/filesystem_helper.hpp"
 #include "rcpputils/env.hpp"
@@ -99,3 +100,41 @@ TEST(TestFilesystemHelper, create_temporary_directory)
     EXPECT_EQ(tmpdir_template_in_name.filename().string().rfind("base_", 0), 0u);
   }
 }
+
+TEST(TestFilesystemHelper, create_temporary_directory_default_parent)
+{
+  // When no parent_path is provided the function should use std::filesystem::temp_directory_path.
+  const auto tmpdir = rcpputils::fs::create_temporary_directory("default_parent_test");
+  EXPECT_TRUE(std::filesystem::exists(tmpdir));
+  EXPECT_TRUE(std::filesystem::is_directory(tmpdir));
+  // The parent must be the system temp directory.
+  // Normalize both sides to remove any trailing separator before comparing
+  // (std::filesystem::temp_directory_path() appends a trailing slash on Windows
+  // while path::parent_path() does not).
+  const std::filesystem::path expected_parent =
+    std::filesystem::path(std::filesystem::temp_directory_path().generic_string());
+  const std::filesystem::path actual_parent =
+    std::filesystem::path(tmpdir.parent_path().generic_string());
+  EXPECT_EQ(actual_parent, expected_parent);
+  EXPECT_TRUE(std::filesystem::remove_all(tmpdir));
+}
+
+TEST(TestFilesystemHelper, create_temporary_directory_unique_per_call)
+{
+  // Multiple calls with the same base_name must produce different paths.
+  constexpr int kNumDirs = 5;
+  std::vector<std::filesystem::path> dirs;
+  dirs.reserve(kNumDirs);
+  for (int i = 0; i < kNumDirs; ++i) {
+    dirs.push_back(rcpputils::fs::create_temporary_directory("unique_test"));
+  }
+  // All paths must be distinct.
+  for (int i = 0; i < kNumDirs; ++i) {
+    for (int j = i + 1; j < kNumDirs; ++j) {
+      EXPECT_NE(dirs[i], dirs[j]);
+    }
+  }
+  for (const auto & d : dirs) {
+    std::filesystem::remove_all(d);
+  }
+}
diff --git a/test/test_process.cpp b/test/test_process.cpp
index 9b276c7..74350c3 100644
--- a/test/test_process.cpp
+++ b/test/test_process.cpp
@@ -21,3 +21,8 @@
 TEST(TestProcess, test_get_executable_name) {
   EXPECT_EQ("test_process", rcpputils::get_executable_name());
 }
+
+TEST(TestProcess, test_get_executable_name_consistent) {
+  // Calling twice must return the same value.
+  EXPECT_EQ(rcpputils::get_executable_name(), rcpputils::get_executable_name());
+}
diff --git a/test/test_shared_library.cpp b/test/test_shared_library.cpp
index 328a33f..3b992a1 100644
--- a/test/test_shared_library.cpp
+++ b/test/test_shared_library.cpp
@@ -82,6 +82,47 @@ TEST(test_shared_library, failed_test) {
   }
 }
 
+TEST(test_shared_library, has_symbol_string_overload) {
+  const std::string library_name = rcpputils::get_platform_library_name("dummy_shared_library");
+  auto library = std::make_shared<rcpputils::SharedLibrary>(library_name);
+
+  // Positive: string overload delegates to const char* overload.
+  EXPECT_TRUE(library->has_symbol(std::string("print_name")));
+
+  // Negative: missing symbol via string overload.
+  EXPECT_FALSE(library->has_symbol(std::string("nonexistent_symbol_xyz")));
+}
+
+TEST(test_shared_library, get_symbol_string_overload_throws_on_missing) {
+  const std::string library_name = rcpputils::get_platform_library_name("dummy_shared_library");
+  auto library = std::make_shared<rcpputils::SharedLibrary>(library_name);
+
+  EXPECT_THROW(
+    library->get_symbol(std::string("nonexistent_symbol_xyz")),
+    std::runtime_error);
+}
+
+TEST(test_shared_library, get_library_path_non_empty) {
+  const std::string library_name = rcpputils::get_platform_library_name("dummy_shared_library");
+  auto library = std::make_shared<rcpputils::SharedLibrary>(library_name);
+  EXPECT_FALSE(library->get_library_path().empty());
+}
+
+TEST(test_get_platform_library_name, release_name_contains_library_name) {
+  const std::string name = rcpputils::get_platform_library_name("mylib", false);
+  EXPECT_NE(name.find("mylib"), std::string::npos);
+  EXPECT_FALSE(name.empty());
+}
+
+TEST(test_get_platform_library_name, debug_and_release_differ_or_equal) {
+  // On some platforms (e.g. Windows) debug builds append a 'd' suffix.
+  // We only verify both calls succeed and return non-empty strings.
+  const std::string release_name = rcpputils::get_platform_library_name("mylib", false);
+  const std::string debug_name = rcpputils::get_platform_library_name("mylib", true);
+  EXPECT_FALSE(release_name.empty());
+  EXPECT_FALSE(debug_name.empty());
+}
+
 TEST(test_get_platform_library_name, failed_test) {
   // create a string bigger than the internal buffer
   std::string str(2000, 'A');
diff --git a/test/test_thread_name.cpp b/test/test_thread_name.cpp
index 53da149..4acf633 100644
--- a/test/test_thread_name.cpp
+++ b/test/test_thread_name.cpp
@@ -22,6 +22,19 @@ TEST(TestOsThread, set_thread_name) {
   EXPECT_STREQ("test_thread", rcpputils::get_thread_name().c_str());
 }
 
+TEST(TestOsThread, set_thread_name_empty) {
+  // Setting an empty name must not throw and get_thread_name must return empty string.
+  EXPECT_NO_THROW(rcpputils::set_thread_name(""));
+  EXPECT_STREQ("", rcpputils::get_thread_name().c_str());
+}
+
+TEST(TestOsThread, get_thread_name_returns_string) {
+  rcpputils::set_thread_name("abc");
+  const std::string name = rcpputils::get_thread_name();
+  EXPECT_FALSE(name.empty());
+  EXPECT_STREQ("abc", name.c_str());
+}
+
 #if defined(_WIN32)
 TEST(TestOsThread, no_truncation_on_windows) {
   rcpputils::set_thread_name("0123456789abcdef");
@@ -29,6 +42,13 @@ TEST(TestOsThread, no_truncation_on_windows) {
   // Should be unaffected by truncation
   EXPECT_STREQ("0123456789abcdef", rcpputils::get_thread_name().c_str());
 }
+
+TEST(TestOsThread, exact_max_length_no_truncation_windows) {
+  // 15 chars is well within the Windows limit; no truncation expected.
+  const std::string name_15(15, 'x');
+  rcpputils::set_thread_name(name_15);
+  EXPECT_EQ(rcpputils::get_thread_name(), name_15);
+}
 #elif defined(__APPLE__)
 TEST(TestOsThread, truncation_on_apple) {
   rcpputils::set_thread_name(
@@ -38,6 +58,13 @@ TEST(TestOsThread, truncation_on_apple) {
   EXPECT_STREQ("0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcde",
     rcpputils::get_thread_name().c_str());
 }
+
+TEST(TestOsThread, exact_max_length_no_truncation_apple) {
+  // Exactly 63 chars (MAXTHREADNAMESIZE - 1): must not be truncated.
+  const std::string name_63(63, 'y');
+  rcpputils::set_thread_name(name_63);
+  EXPECT_EQ(rcpputils::get_thread_name(), name_63);
+}
 #else  // posix
 TEST(TestOsThread, truncation_on_posix) {
   rcpputils::set_thread_name("0123456789abcdef");
@@ -45,4 +72,18 @@ TEST(TestOsThread, truncation_on_posix) {
   // Should be 15 characters and then the null terminator
   EXPECT_STREQ("0123456789abcde", rcpputils::get_thread_name().c_str());
 }
+
+TEST(TestOsThread, exact_max_length_no_truncation_posix) {
+  // Exactly 15 chars (MAXTHREADNAMESIZE - 1): must not be truncated.
+  const std::string name_15(15, 'z');
+  rcpputils::set_thread_name(name_15);
+  EXPECT_EQ(rcpputils::get_thread_name(), name_15);
+}
+
+TEST(TestOsThread, one_less_than_max_no_truncation_posix) {
+  // 14 chars is under the limit; returned name must be identical.
+  const std::string name_14(14, 'w');
+  rcpputils::set_thread_name(name_14);
+  EXPECT_EQ(rcpputils::get_thread_name(), name_14);
+}
 #endif