12 files changed, 1030 insertions, 0 deletions
diff --git a/nihil/tests/CMakeLists.txt b/nihil/tests/CMakeLists.txt
new file mode 100644
index 0000000..abeab88
--- /dev/null
+++ b/nihil/tests/CMakeLists.txt
@@ -0,0 +1,25 @@
+# This source code is released into the public domain.
+
+add_executable(nihil.test
+	command_map.cc
+	ctype.cc
+	fd.cc
+	generator.cc
+	generic_error.cc
+	getenv.cc
+	guard.cc
+	next_word.cc
+	skipws.cc
+	spawn.cc
+	tabulate.cc)
+
+target_link_libraries(nihil.test PRIVATE
+	nihil
+	Catch2::Catch2WithMain
+)
+
+find_package(Catch2 REQUIRED)
+
+include(CTest)
+include(Catch)
+catch_discover_tests(nihil.test)
diff --git a/nihil/tests/command_map.cc b/nihil/tests/command_map.cc
new file mode 100644
index 0000000..75b6f0d
--- /dev/null
+++ b/nihil/tests/command_map.cc
@@ -0,0 +1,41 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+#include <vector>
+
+#include <catch2/catch_test_macros.hpp>
+
+import nihil;
+
+namespace {
+
+auto cmd_sub1_called = false;
+auto cmd_sub1 = nihil::command<int>("cmd sub1", [](int, int, char **) -> int
+{
+	cmd_sub1_called = true;
+	return 0;
+});
+
+} // anonymous namespace
+
+TEST_CASE("command_map: basic", "[command_map]")
+{
+	auto args = std::vector<char const *>{
+		"cmd", "sub1", nullptr
+	};
+	auto argv = const_cast<char **>(args.data());
+	nihil::dispatch_command(0, args.size(), argv);
+	REQUIRE(cmd_sub1_called == true);
+}
+
+TEST_CASE("command_map: unknown command", "[command_map]")
+{
+	auto args = std::vector<char const *>{
+		"cmd", "nonesuch", nullptr
+	};
+	auto argv = const_cast<char **>(args.data());
+
+	REQUIRE_THROWS_AS(nihil::dispatch_command(0, args.size(), argv),
+			  nihil::usage_error);
+}
diff --git a/nihil/tests/ctype.cc b/nihil/tests/ctype.cc
new file mode 100644
index 0000000..87f5103
--- /dev/null
+++ b/nihil/tests/ctype.cc
@@ -0,0 +1,373 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+#include <catch2/catch_test_macros.hpp>
+
+import nihil;
+
+TEST_CASE("ctype: space", "[ctype]") {
+	auto is_utf8_space =
+		nihil::ctype_is(std::ctype_base::space,
+				std::locale("C.UTF-8"));
+
+	// '\v' (vertical tab) is a space
+	REQUIRE(nihil::is_space('\v') == true);
+	REQUIRE(nihil::is_space(L'\v') == true);
+
+	REQUIRE(nihil::is_c_space('\v') == true);
+	REQUIRE(nihil::is_c_space(L'\v') == true);
+
+	REQUIRE(is_utf8_space('\v') == true);
+	REQUIRE(is_utf8_space(L'\v') == true);
+
+	// 'x' is not a space
+	REQUIRE(nihil::is_space('x') == false);
+	REQUIRE(nihil::is_space(L'x') == false);
+
+	REQUIRE(nihil::is_c_space('x') == false);
+	REQUIRE(nihil::is_c_space(L'x') == false);
+
+	REQUIRE(is_utf8_space('x') == false);
+	REQUIRE(is_utf8_space(L'x') == false);
+
+	// U+2003 EM SPACE is a space
+	REQUIRE(nihil::is_space(L'\u2003') == false);
+	REQUIRE(nihil::is_c_space(L'\u2003') == false);
+	REQUIRE(is_utf8_space(L'\u2003') == true);
+}
+
+TEST_CASE("ctype: print", "[ctype]") {
+	auto is_utf8_print =
+		nihil::ctype_is(std::ctype_base::print,
+				std::locale("C.UTF-8"));
+
+	// 'x' is printable
+	REQUIRE(nihil::is_print('x') == true);
+	REQUIRE(nihil::is_print(L'x') == true);
+
+	REQUIRE(nihil::is_c_print('x') == true);
+	REQUIRE(nihil::is_c_print(L'x') == true);
+
+	REQUIRE(is_utf8_print('x') == true);
+	REQUIRE(is_utf8_print(L'x') == true);
+
+	// '\003' is not printable
+	REQUIRE(nihil::is_print('\003') == false);
+	REQUIRE(nihil::is_print(L'\003') == false);
+
+	REQUIRE(nihil::is_c_print('\003') == false);
+	REQUIRE(nihil::is_c_print(L'\003') == false);
+
+	REQUIRE(is_utf8_print('\003') == false);
+	REQUIRE(is_utf8_print(L'\003') == false);
+
+	// U+0410 CYRILLIC CAPITAL LETTER A is printable
+	REQUIRE(nihil::is_print(L'\u0410') == false);
+	REQUIRE(nihil::is_c_print(L'\u0410') == false);
+	REQUIRE(is_utf8_print(L'\u0410') == true);
+}
+
+TEST_CASE("ctype: cntrl", "[ctype]") {
+	auto is_utf8_cntrl =
+		nihil::ctype_is(std::ctype_base::cntrl,
+				std::locale("C.UTF-8"));
+
+	// '\003' is a control character
+	REQUIRE(nihil::is_cntrl('\003') == true);
+	REQUIRE(nihil::is_cntrl(L'\003') == true);
+
+	REQUIRE(nihil::is_c_cntrl('\003') == true);
+	REQUIRE(nihil::is_c_cntrl(L'\003') == true);
+
+	REQUIRE(is_utf8_cntrl('\003') == true);
+	REQUIRE(is_utf8_cntrl(L'\003') == true);
+
+
+	// 'x' is not a control character
+	REQUIRE(nihil::is_cntrl('x') == false);
+	REQUIRE(nihil::is_cntrl(L'x') == false);
+
+	REQUIRE(nihil::is_c_cntrl('x') == false);
+	REQUIRE(nihil::is_c_cntrl(L'x') == false);
+
+	REQUIRE(is_utf8_cntrl('x') == false);
+	REQUIRE(is_utf8_cntrl(L'x') == false);
+
+	// U+00AD SOFT HYPHEN is a control character.
+	REQUIRE(nihil::is_cntrl(L'\u00ad') == false);
+	REQUIRE(nihil::is_c_cntrl(L'\u00ad') == false);
+	REQUIRE(is_utf8_cntrl(L'\u00ad') == true);
+}
+
+TEST_CASE("ctype: upper", "[ctype]") {
+	auto is_utf8_upper =
+		nihil::ctype_is(std::ctype_base::upper,
+				std::locale("C.UTF-8"));
+
+	// 'A' is upper case
+	REQUIRE(nihil::is_upper('A') == true);
+	REQUIRE(nihil::is_upper(L'A') == true);
+
+	REQUIRE(nihil::is_c_upper('A') == true);
+	REQUIRE(nihil::is_c_upper(L'A') == true);
+
+	REQUIRE(is_utf8_upper('A') == true);
+	REQUIRE(is_utf8_upper(L'A') == true);
+
+	// 'a' is not upper case
+	REQUIRE(nihil::is_upper('a') == false);
+	REQUIRE(nihil::is_upper(L'a') == false);
+
+	REQUIRE(nihil::is_c_upper('a') == false);
+	REQUIRE(nihil::is_c_upper(L'a') == false);
+
+	REQUIRE(is_utf8_upper('a') == false);
+	REQUIRE(is_utf8_upper(L'a') == false);
+
+	// U+0410 CYRILLIC CAPITAL LETTER A is upper case
+	REQUIRE(nihil::is_upper(L'\u0410') == false);
+	REQUIRE(nihil::is_c_upper(L'\u0410') == false);
+	REQUIRE(is_utf8_upper(L'\u0410') == true);
+}
+
+TEST_CASE("ctype: lower", "[ctype]") {
+	auto is_utf8_lower =
+		nihil::ctype_is(std::ctype_base::lower,
+				std::locale("C.UTF-8"));
+
+	// 'a' is lower case
+	REQUIRE(nihil::is_lower('a') == true);
+	REQUIRE(nihil::is_lower(L'a') == true);
+
+	REQUIRE(nihil::is_c_lower('a') == true);
+	REQUIRE(nihil::is_c_lower(L'a') == true);
+
+	REQUIRE(is_utf8_lower('a') == true);
+	REQUIRE(is_utf8_lower(L'a') == true);
+
+	// 'A' is not lower case
+	REQUIRE(nihil::is_lower('A') == false);
+	REQUIRE(nihil::is_lower(L'A') == false);
+
+	REQUIRE(nihil::is_c_lower('A') == false);
+	REQUIRE(nihil::is_c_lower(L'A') == false);
+
+	REQUIRE(is_utf8_lower('A') == false);
+	REQUIRE(is_utf8_lower(L'A') == false);
+
+	// U+0430 CYRILLIC SMALL LETTER A
+	REQUIRE(nihil::is_lower(L'\u0430') == false);
+	REQUIRE(nihil::is_c_lower(L'\u0430') == false);
+	REQUIRE(is_utf8_lower(L'\u0430') == true);
+}
+
+TEST_CASE("ctype: alpha", "[ctype]") {
+	auto is_utf8_alpha =
+		nihil::ctype_is(std::ctype_base::alpha,
+				std::locale("C.UTF-8"));
+
+	// 'a' is alphabetical
+	REQUIRE(nihil::is_alpha('a') == true);
+	REQUIRE(nihil::is_alpha(L'a') == true);
+
+	REQUIRE(nihil::is_c_alpha('a') == true);
+	REQUIRE(nihil::is_c_alpha(L'a') == true);
+
+	REQUIRE(is_utf8_alpha('a') == true);
+	REQUIRE(is_utf8_alpha(L'a') == true);
+
+	// '1' is not alphabetical
+	REQUIRE(nihil::is_alpha('1') == false);
+	REQUIRE(nihil::is_alpha(L'1') == false);
+
+	REQUIRE(nihil::is_c_alpha('1') == false);
+	REQUIRE(nihil::is_c_alpha(L'1') == false);
+
+	REQUIRE(is_utf8_alpha('1') == false);
+	REQUIRE(is_utf8_alpha(L'1') == false);
+
+	// U+0430 CYRILLIC SMALL LETTER A
+	REQUIRE(nihil::is_alpha(L'\u0430') == false);
+	REQUIRE(nihil::is_c_alpha(L'\u0430') == false);
+	REQUIRE(is_utf8_alpha(L'\u0430') == true);
+}
+
+TEST_CASE("ctype: digit", "[ctype]") {
+	auto is_utf8_digit =
+		nihil::ctype_is(std::ctype_base::digit,
+				std::locale("C.UTF-8"));
+
+	// '1' is a digit
+	REQUIRE(nihil::is_digit('1') == true);
+	REQUIRE(nihil::is_digit(L'1') == true);
+
+	REQUIRE(nihil::is_c_digit('1') == true);
+	REQUIRE(nihil::is_c_digit(L'1') == true);
+
+	REQUIRE(is_utf8_digit('1') == true);
+	REQUIRE(is_utf8_digit(L'1') == true);
+
+	// 'a' is not a digit
+	REQUIRE(nihil::is_digit('a') == false);
+	REQUIRE(nihil::is_digit(L'a') == false);
+
+	REQUIRE(nihil::is_c_digit('a') == false);
+	REQUIRE(nihil::is_c_digit(L'a') == false);
+
+	REQUIRE(is_utf8_digit('a') == false);
+	REQUIRE(is_utf8_digit(L'a') == false);
+
+	// U+0660 ARABIC-INDIC DIGIT ZERO
+	REQUIRE(nihil::is_digit(L'\u0660') == false);
+	REQUIRE(nihil::is_c_digit(L'\u0660') == false);
+	REQUIRE(is_utf8_digit(L'\u0660') == true);
+}
+
+TEST_CASE("ctype: punct", "[ctype]") {
+	auto is_utf8_punct =
+		nihil::ctype_is(std::ctype_base::punct,
+				std::locale("C.UTF-8"));
+
+	// ';' is punctuation
+	REQUIRE(nihil::is_punct(';') == true);
+	REQUIRE(nihil::is_punct(L';') == true);
+
+	REQUIRE(nihil::is_c_punct(';') == true);
+	REQUIRE(nihil::is_c_punct(L';') == true);
+
+	REQUIRE(is_utf8_punct(';') == true);
+	REQUIRE(is_utf8_punct(L';') == true);
+
+	// 'a' is not punctuation
+	REQUIRE(nihil::is_punct('a') == false);
+	REQUIRE(nihil::is_punct(L'a') == false);
+
+	REQUIRE(nihil::is_c_punct('a') == false);
+	REQUIRE(nihil::is_c_punct(L'a') == false);
+
+	REQUIRE(is_utf8_punct('a') == false);
+	REQUIRE(is_utf8_punct(L'a') == false);
+
+	// U+00A1 INVERTED EXCLAMATION MARK
+	REQUIRE(nihil::is_punct(L'\u00A1') == false);
+	REQUIRE(nihil::is_c_punct(L'\u00A1') == false);
+	REQUIRE(is_utf8_punct(L'\u00A1') == true);
+}
+
+TEST_CASE("ctype: xdigit", "[ctype]") {
+	auto is_utf8_xdigit =
+		nihil::ctype_is(std::ctype_base::xdigit,
+				std::locale("C.UTF-8"));
+
+	// 'f' is an xdigit
+	REQUIRE(nihil::is_xdigit('f') == true);
+	REQUIRE(nihil::is_xdigit(L'f') == true);
+
+	REQUIRE(nihil::is_c_xdigit('f') == true);
+	REQUIRE(nihil::is_c_xdigit(L'f') == true);
+
+	REQUIRE(is_utf8_xdigit('f') == true);
+	REQUIRE(is_utf8_xdigit(L'f') == true);
+
+	// 'g' is not an xdigit
+	REQUIRE(nihil::is_xdigit('g') == false);
+	REQUIRE(nihil::is_xdigit(L'g') == false);
+
+	REQUIRE(nihil::is_c_xdigit('g') == false);
+	REQUIRE(nihil::is_c_xdigit(L'g') == false);
+
+	REQUIRE(is_utf8_xdigit('g') == false);
+	REQUIRE(is_utf8_xdigit(L'g') == false);
+}
+
+TEST_CASE("ctype: blank", "[ctype]") {
+	auto is_utf8_blank =
+		nihil::ctype_is(std::ctype_base::blank,
+				std::locale("C.UTF-8"));
+
+	// '\t' is a blank
+	REQUIRE(nihil::is_blank('\t') == true);
+	REQUIRE(nihil::is_blank(L'\t') == true);
+
+	REQUIRE(nihil::is_c_blank('\t') == true);
+	REQUIRE(nihil::is_c_blank(L'\t') == true);
+
+	REQUIRE(is_utf8_blank('\t') == true);
+	REQUIRE(is_utf8_blank(L'\t') == true);
+
+	// '\v' is not a blank
+	REQUIRE(nihil::is_blank('\v') == false);
+	REQUIRE(nihil::is_blank(L'\v') == false);
+
+	REQUIRE(nihil::is_c_blank('\v') == false);
+	REQUIRE(nihil::is_c_blank(L'\v') == false);
+
+	REQUIRE(is_utf8_blank('\v') == false);
+	REQUIRE(is_utf8_blank(L'\v') == false);
+
+	// There don't seem to be any UTF-8 blank characters, at least
+	// in FreeBSD libc.
+}
+
+TEST_CASE("ctype: alnum", "[ctype]") {
+	auto is_utf8_alnum =
+		nihil::ctype_is(std::ctype_base::alnum,
+				std::locale("C.UTF-8"));
+
+	// 'a' is alphanumeric
+	REQUIRE(nihil::is_alnum('a') == true);
+	REQUIRE(nihil::is_alnum(L'a') == true);
+
+	REQUIRE(nihil::is_c_alnum('a') == true);
+	REQUIRE(nihil::is_c_alnum(L'a') == true);
+
+	REQUIRE(is_utf8_alnum('a') == true);
+	REQUIRE(is_utf8_alnum(L'a') == true);
+
+	// '\t' is not a alnum
+	REQUIRE(nihil::is_alnum('\t') == false);
+	REQUIRE(nihil::is_alnum(L'\t') == false);
+
+	REQUIRE(nihil::is_c_alnum('\t') == false);
+	REQUIRE(nihil::is_c_alnum(L'\t') == false);
+
+	REQUIRE(is_utf8_alnum('\t') == false);
+	REQUIRE(is_utf8_alnum(L'\t') == false);
+
+	// U+0430 CYRILLIC SMALL LETTER A
+	REQUIRE(nihil::is_alnum(L'\u0430') == false);
+	REQUIRE(nihil::is_c_alnum(L'\u0430') == false);
+	REQUIRE(is_utf8_alnum(L'\u0430') == true);
+}
+
+TEST_CASE("ctype: graph", "[ctype]") {
+	auto is_utf8_graph =
+		nihil::ctype_is(std::ctype_base::graph,
+				std::locale("C.UTF-8"));
+
+	// 'a' is graphical 
+	REQUIRE(nihil::is_graph('a') == true);
+	REQUIRE(nihil::is_graph(L'a') == true);
+
+	REQUIRE(nihil::is_c_graph('a') == true);
+	REQUIRE(nihil::is_c_graph(L'a') == true);
+
+	REQUIRE(is_utf8_graph('a') == true);
+	REQUIRE(is_utf8_graph(L'a') == true);
+
+	// '\t' is not graphical
+	REQUIRE(nihil::is_graph('\t') == false);
+	REQUIRE(nihil::is_graph(L'\t') == false);
+
+	REQUIRE(nihil::is_c_graph('\t') == false);
+	REQUIRE(nihil::is_c_graph(L'\t') == false);
+
+	REQUIRE(is_utf8_graph('\t') == false);
+	REQUIRE(is_utf8_graph(L'\t') == false);
+
+	// U+0430 CYRILLIC SMALL LETTER A
+	REQUIRE(nihil::is_graph(L'\u0430') == false);
+	REQUIRE(nihil::is_c_graph(L'\u0430') == false);
+	REQUIRE(is_utf8_graph(L'\u0430') == true);
+}
diff --git a/nihil/tests/fd.cc b/nihil/tests/fd.cc
new file mode 100644
index 0000000..fbf353e
--- /dev/null
+++ b/nihil/tests/fd.cc
@@ -0,0 +1,200 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+#include <span>
+
+#include <stdio.h>
+#include <fcntl.h>
+
+#include <catch2/catch_test_macros.hpp>
+
+import nihil;
+
+using namespace std::literals;
+
+namespace {
+
+// Test if an fd is open.
+auto fd_is_open(int fd) -> bool {
+	auto const ret = ::fcntl(fd, F_GETFL);
+	return ret == 0;
+}
+
+} // anonymous namespace
+
+TEST_CASE("fd: construct empty", "[fd]") {
+	nihil::fd fd;
+
+	REQUIRE(!fd);
+	REQUIRE_THROWS_AS(fd.get(), nihil::fd_logic_error);
+}
+
+TEST_CASE("fd: construct from fd", "[fd]") {
+	auto file = ::open("/dev/null", O_RDONLY);
+	REQUIRE(file > 0);
+
+	{
+		auto fd = nihil::fd(file);
+		REQUIRE(fd_is_open(fd.get()));
+	}
+
+	REQUIRE(!fd_is_open(file));
+}
+
+TEST_CASE("fd: close", "[fd]") {
+	auto file = ::open("/dev/null", O_RDONLY);
+	REQUIRE(file > 0);
+
+	auto fd = nihil::fd(file);
+	REQUIRE(fd);
+
+	auto const ret = fd.close();
+	REQUIRE(ret);
+	REQUIRE(!fd_is_open(file));
+}
+
+TEST_CASE("fd: move construct", "[fd]") {
+	auto file = ::open("/dev/null", O_RDONLY);
+	REQUIRE(file > 0);
+
+	auto fd1 = nihil::fd(file);
+	REQUIRE(fd_is_open(fd1.get()));
+
+	auto fd2(std::move(fd1));
+	REQUIRE(!fd1);
+	REQUIRE(fd2);
+	REQUIRE(fd2.get() == file);
+	REQUIRE(fd_is_open(file));
+}
+
+TEST_CASE("fd: move assign", "[fd]") {
+	auto file = ::open("/dev/null", O_RDONLY);
+	REQUIRE(file > 0);
+
+	auto fd1 = nihil::fd(file);
+	REQUIRE(fd_is_open(fd1.get()));
+
+	auto fd2 = nihil::fd();
+	REQUIRE(!fd2);
+
+	fd2 = std::move(fd1);
+
+	REQUIRE(!fd1);
+	REQUIRE(fd2);
+	REQUIRE(fd2.get() == file);
+	REQUIRE(fd_is_open(file));
+}
+
+TEST_CASE("fd: release", "[fd]") {
+	auto file = ::open("/dev/null", O_RDONLY);
+	REQUIRE(file > 0);
+
+	auto fd = nihil::fd(file);
+	auto fdesc = std::move(fd).release();
+	REQUIRE(!fd);
+	REQUIRE(fdesc == file);
+}
+
+TEST_CASE("fd: dup", "[fd]") {
+	auto file = ::open("/dev/null", O_RDONLY);
+	REQUIRE(file > 0);
+
+	auto fd = nihil::fd(file);
+	REQUIRE(fd);
+
+	auto fd2 = dup(fd);
+	REQUIRE(fd2);
+	REQUIRE(fd.get() != fd2->get());
+}
+
+TEST_CASE("fd: dup2", "[fd]") {
+	auto file = ::open("/dev/null", O_RDONLY);
+	REQUIRE(file > 0);
+
+	REQUIRE(!fd_is_open(666));
+
+	auto fd = nihil::fd(file);
+	auto fd2 = dup(fd, 666);
+
+	REQUIRE(fd);
+	REQUIRE(fd2);
+	REQUIRE(fd2->get() == 666);
+}
+
+TEST_CASE("fd: flags", "[fd]") {
+	auto file = ::open("/dev/null", O_RDONLY);
+	REQUIRE(file > 0);
+
+	auto fd = nihil::fd(file);
+
+	{
+		auto const ret = replaceflags(fd, 0);
+		REQUIRE(ret);
+		REQUIRE(getflags(fd) == 0);
+	}
+
+	{
+		auto const ret = setflags(fd, O_NONBLOCK);
+		REQUIRE(ret == O_NONBLOCK);
+		REQUIRE(getflags(fd) == O_NONBLOCK);
+	}
+
+	{
+		auto const ret = setflags(fd, O_SYNC);
+		REQUIRE(ret == (O_NONBLOCK|O_SYNC));
+		REQUIRE(getflags(fd) == (O_NONBLOCK|O_SYNC));
+	}
+
+	{
+		auto const ret = clearflags(fd, O_NONBLOCK);
+		REQUIRE(ret == O_SYNC);
+		REQUIRE(getflags(fd) == O_SYNC);
+	}
+}
+
+TEST_CASE("fd: fdflags", "[fd]") {
+	auto file = ::open("/dev/null", O_RDONLY);
+	REQUIRE(file > 0);
+
+	auto fd = nihil::fd(file);
+
+	{
+		auto const ret = replacefdflags(fd, 0);
+		REQUIRE(ret);
+		REQUIRE(getfdflags(fd) == 0);
+	}
+
+	{
+		auto const ret = setfdflags(fd, FD_CLOEXEC);
+		REQUIRE(ret == FD_CLOEXEC);
+		REQUIRE(getfdflags(fd) == FD_CLOEXEC);
+	}
+
+	{
+		auto const ret = clearfdflags(fd, FD_CLOEXEC);
+		REQUIRE(ret == 0);
+		REQUIRE(getfdflags(fd) == 0);
+	}
+}
+
+TEST_CASE("fd: pipe, read, write", "[fd]") {
+	auto fds = nihil::pipe();
+	REQUIRE(fds);
+
+	auto [fd1, fd2] = std::move(*fds);
+
+	auto constexpr test_string = "test string"sv;
+
+	auto ret = write(fd1, test_string);
+	REQUIRE(ret);
+	REQUIRE(*ret == test_string.size());
+
+	auto readbuf = std::array<char, test_string.size() * 2>{};
+	ret = read(fd2, readbuf);
+	REQUIRE(ret);
+	REQUIRE(*ret == test_string.size());
+
+	auto read_string = std::string_view(std::span(readbuf).subspan(0, *ret));
+	REQUIRE(read_string == test_string);
+}
diff --git a/nihil/tests/generator.cc b/nihil/tests/generator.cc
new file mode 100644
index 0000000..8657756
--- /dev/null
+++ b/nihil/tests/generator.cc
@@ -0,0 +1,56 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+#include <coroutine>
+#include <ranges>
+#include <vector>
+
+#include <catch2/catch_test_macros.hpp>
+
+import nihil;
+
+TEST_CASE("generator: basic", "[generator]") 
+{
+	auto fn = [] () -> nihil::generator<int> {
+		co_yield 1;
+		co_yield 2;
+		co_yield 3;
+	};
+
+	auto values = std::vector<int>();
+	std::ranges::copy(fn(), std::back_inserter(values));
+
+	REQUIRE(values == std::vector{1, 2, 3});
+}
+
+TEST_CASE("generator: exceptions", "[generator]") 
+{
+	auto fn = [] () -> nihil::generator<int> {
+		co_yield 1;
+		throw std::runtime_error("test");
+	};
+
+	auto range = fn();
+	auto it = std::ranges::begin(range);
+	REQUIRE(*it == 1);
+	REQUIRE_THROWS_AS(it++, std::runtime_error);
+}
+
+TEST_CASE("generator: elements_of", "[generator]") 
+{
+	auto fn1 = [] -> nihil::generator<int> {
+		co_yield 1;
+		co_yield 2;
+		co_yield 3;
+	};
+
+	auto fn2 = [&fn1] -> nihil::generator<int> {
+		co_yield nihil::ranges::elements_of(fn1());
+	};
+
+	auto values = std::vector<int>();
+	std::ranges::copy(fn2(), std::back_inserter(values));
+
+	REQUIRE(values == std::vector{1, 2, 3});
+}
diff --git a/nihil/tests/generic_error.cc b/nihil/tests/generic_error.cc
new file mode 100644
index 0000000..b213af9
--- /dev/null
+++ b/nihil/tests/generic_error.cc
@@ -0,0 +1,17 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+#include <catch2/catch_test_macros.hpp>
+
+import nihil;
+
+using namespace std::literals;
+
+TEST_CASE("generic_error: basic", "[generic_error]") {
+	try {
+		throw nihil::generic_error("{} + {} = {}", 1, 2, 3);
+	} catch (nihil::generic_error const &exc) {
+		REQUIRE(exc.what() == "1 + 2 = 3"s);
+	}
+}
diff --git a/nihil/tests/getenv.cc b/nihil/tests/getenv.cc
new file mode 100644
index 0000000..adfa84f
--- /dev/null
+++ b/nihil/tests/getenv.cc
@@ -0,0 +1,48 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+#include <ranges>
+#include <string>
+
+#include <unistd.h>
+
+#include <catch2/catch_test_macros.hpp>
+
+import nihil;
+
+TEST_CASE("getenv: existing value", "[getenv]")
+{
+	auto constexpr *name = "LFJAIL_TEST_VAR";
+	auto constexpr *value = "test is a test";
+
+	REQUIRE(::setenv(name, value, 1) == 0);
+
+	auto const s = nihil::getenv(name);
+	REQUIRE(s);
+	REQUIRE(*s == value);
+}
+
+TEST_CASE("getenv: non-existing value", "[getenv]")
+{
+	auto constexpr *name = "LFJAIL_TEST_VAR";
+
+	REQUIRE(::unsetenv(name) == 0);
+
+	auto const s = nihil::getenv(name);
+	REQUIRE(!s);
+	REQUIRE(s.error() == std::errc::no_such_file_or_directory);
+}
+
+// Force the call to getenv_r() to reallocate.
+TEST_CASE("getenv: long value")
+{
+	auto constexpr *name = "LFJAIL_TEST_VAR";
+	auto const value = std::string(4096, 'a');
+
+	REQUIRE(::setenv(name, value.c_str(), 1) == 0);
+
+	auto const s = nihil::getenv(name);
+	REQUIRE(s);
+	REQUIRE(*s == value);
+}
diff --git a/nihil/tests/guard.cc b/nihil/tests/guard.cc
new file mode 100644
index 0000000..f88aa9b
--- /dev/null
+++ b/nihil/tests/guard.cc
@@ -0,0 +1,20 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+#include <catch2/catch_test_macros.hpp>
+
+import nihil;
+
+using namespace std::literals;
+
+TEST_CASE("guard: basic", "[guard]") {
+	int n = 0;
+
+	{
+		auto guard = nihil::guard([&] { n = 1; });
+		REQUIRE(n == 0);
+	}
+
+	REQUIRE(n == 1);
+}
diff --git a/nihil/tests/next_word.cc b/nihil/tests/next_word.cc
new file mode 100644
index 0000000..4055485
--- /dev/null
+++ b/nihil/tests/next_word.cc
@@ -0,0 +1,65 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+#include <locale>
+#include <string>
+
+#include <catch2/catch_test_macros.hpp>
+
+import nihil;
+
+TEST_CASE("next_word: basic", "[next_word]")
+{
+	using namespace std::literals;
+	auto s = "foo bar baz"sv;
+
+	auto words = nihil::next_word(s);
+	REQUIRE(words.first == "foo");
+	REQUIRE(words.second == " bar baz");
+
+	auto word = nihil::next_word(&s);
+	REQUIRE(word == "foo");
+	REQUIRE(s == " bar baz");
+}
+
+TEST_CASE("next_word: multiple spaces", "[next_word]")
+{
+	using namespace std::literals;
+	auto s = "foo  bar  baz"sv;
+
+	auto words = nihil::next_word(s);
+	REQUIRE(words.first == "foo");
+	REQUIRE(words.second == "  bar  baz");
+
+	auto word = nihil::next_word(&s);
+	REQUIRE(word == "foo");
+	REQUIRE(s == "  bar  baz");
+}
+
+TEST_CASE("next_word: leading spaces", "[next_word]")
+{
+	using namespace std::literals;
+	auto s = " \tfoo  bar  baz"sv;
+
+	auto words = nihil::next_word(s);
+	REQUIRE(words.first == "foo");
+	REQUIRE(words.second == "  bar  baz");
+
+	auto word = nihil::next_word(&s);
+	REQUIRE(word == "foo");
+	REQUIRE(s == "  bar  baz");
+}
+
+TEST_CASE("next_word: locale", "[next_word]")
+{
+	using namespace std::literals;
+	auto s = L"\u2003foo\u2003bar\u2003baz"sv;
+
+	auto words = nihil::next_word(s);
+	REQUIRE(words.first == s);
+
+	words = nihil::next_word(s, std::locale("C.UTF-8"));
+	REQUIRE(words.first == L"foo");
+	REQUIRE(words.second == L"\u2003bar\u2003baz");
+}
diff --git a/nihil/tests/skipws.cc b/nihil/tests/skipws.cc
new file mode 100644
index 0000000..2159e2e
--- /dev/null
+++ b/nihil/tests/skipws.cc
@@ -0,0 +1,45 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+#include <locale>
+#include <string>
+using namespace std::literals;
+
+#include <catch2/catch_test_macros.hpp>
+
+import nihil;
+
+TEST_CASE("skipws: basic", "[skipws]")
+{
+	REQUIRE(nihil::skipws("foo"sv) == "foo");
+	REQUIRE(nihil::skipws("   foo"sv) == "foo");
+	REQUIRE(nihil::skipws("foo "sv) == "foo ");
+	REQUIRE(nihil::skipws("foo bar"sv) == "foo bar");
+}
+
+TEST_CASE("skipws: pointer", "[skipws]")
+{
+	auto s = "foo"sv;
+	nihil::skipws(&s);
+	REQUIRE(s == "foo");
+
+	s = "   foo"sv;
+	nihil::skipws(&s);
+	REQUIRE(s == "foo");
+
+	s = "foo "sv;
+	nihil::skipws(&s);
+	REQUIRE(s == "foo ");
+
+	s = "foo bar"sv;
+	nihil::skipws(&s);
+	REQUIRE(s == "foo bar");
+}
+
+TEST_CASE("skipws: locale", "[skipws]")
+{
+	// Assume the default locale is C.
+	REQUIRE(nihil::skipws(L"\u2003foo"sv) == L"\u2003foo");
+	REQUIRE(nihil::skipws(L"\u2003foo"sv, std::locale("C.UTF-8")) == L"foo");
+}
diff --git a/nihil/tests/spawn.cc b/nihil/tests/spawn.cc
new file mode 100644
index 0000000..455223e
--- /dev/null
+++ b/nihil/tests/spawn.cc
@@ -0,0 +1,65 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+#include <catch2/catch_test_macros.hpp>
+
+import nihil;
+
+TEST_CASE("spawn: system", "[spawn]") {
+	using namespace nihil;
+	auto output = std::string();
+	auto result = spawn(shell("x=1; echo $x"),
+			    capture(stdout_fileno, output)).wait();
+
+	REQUIRE(result.okay());
+	REQUIRE(output == "1\n");
+}
+
+TEST_CASE("spawn: execv", "[spawn]") {
+	using namespace nihil;
+	auto output = std::string();
+	auto args = argv::from_args({"sh", "-c", "x=1; echo $x"});
+	auto result = spawn(execv("/bin/sh", std::move(args)),
+			    capture(stdout_fileno, output)).wait();
+
+	REQUIRE(result.okay());
+	REQUIRE(output == "1\n");
+}
+
+TEST_CASE("spawn: execvp", "[spawn]") {
+	using namespace nihil;
+	auto output = std::string();
+	auto args = argv::from_args({"sh", "-c", "x=1; echo $x"});
+	auto result = spawn(execvp("sh", std::move(args)),
+			    capture(stdout_fileno, output)).wait();
+
+	REQUIRE(result.okay());
+	REQUIRE(output == "1\n");
+}
+
+TEST_CASE("spawn: execl", "[spawn]") {
+	using namespace nihil;
+	auto output = std::string();
+	auto result = spawn(execl("/bin/sh", "sh", "-c", "x=1; echo $x"),
+			    capture(stdout_fileno, output)).wait();
+
+	REQUIRE(result.okay());
+	REQUIRE(output == "1\n");
+}
+
+TEST_CASE("spawn: execlp", "[spawn]") {
+	using namespace nihil;
+	auto output = std::string();
+	auto result = spawn(execlp("sh", "sh", "-c", "x=1; echo $x"),
+			    capture(stdout_fileno, output)).wait();
+
+	REQUIRE(result.okay());
+	REQUIRE(output == "1\n");
+}
+
+TEST_CASE("spawn: execlp failure", "[spawn]") {
+	using namespace nihil;
+	REQUIRE_THROWS_AS(execlp("lfjail_nonesuch_executable", "x"),
+			  executable_not_found);
+}
diff --git a/nihil/tests/tabulate.cc b/nihil/tests/tabulate.cc
new file mode 100644
index 0000000..84f8b33
--- /dev/null
+++ b/nihil/tests/tabulate.cc
@@ -0,0 +1,75 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+#include <iterator>
+#include <string>
+#include <vector>
+
+#include <catch2/catch_test_macros.hpp>
+
+import nihil;
+
+using namespace std::literals;
+using namespace nihil;
+
+TEST_CASE("tabulate: basic", "[tabulate]")
+{
+	auto input = std::vector{
+		std::vector{"a",   "foo", "b"},
+		std::vector{"bar", "c",   "baz"},
+	};
+
+	auto result = std::string();
+	tabulate("{:1} {:2} {:3}", input, std::back_inserter(result));
+	REQUIRE(result ==
+"1   2   3\n"
+"a   foo b\n"
+"bar c   baz\n");
+}
+
+TEST_CASE("tabulate: basic wide", "[tabulate]")
+{
+	auto input = std::vector{
+		std::vector{L"a",   L"foo", L"b"},
+		std::vector{L"bar", L"c",   L"baz"},
+	};
+
+	auto result = std::wstring();
+	wtabulate(L"{:1} {:2} {:3}", input, std::back_inserter(result));
+
+	REQUIRE(result ==
+L"1   2   3\n"
+"a   foo b\n"
+"bar c   baz\n");
+}
+
+TEST_CASE("tabulate: jagged", "[tabulate]")
+{
+	auto input = std::vector{
+		std::vector{"a",   "foo", "b"},
+		std::vector{"bar", "baz"},
+	};
+
+	auto result = std::string();
+	tabulate("{:1} {:2} {:3}", input, std::back_inserter(result));
+	REQUIRE(result ==
+"1   2   3\n"
+"a   foo b\n"
+"bar baz\n");
+}
+
+TEST_CASE("tabulate: align", "[tabulate]")
+{
+	auto input = std::vector{
+		std::vector{"a", "longvalue", "s"},
+		std::vector{"a", "s",         "longvalue"},
+	};
+
+	auto result = std::string();
+	tabulate("{:1} {<:2} {>:3}", input, std::back_inserter(result));
+	REQUIRE(result ==
+"1 2                 3\n"
+"a longvalue         s\n"
+"a s         longvalue\n");
+}