diff --git a/build.sh b/build.sh
index c34da5c..d2175bb 100755
--- a/build.sh
+++ b/build.sh
@@ -15,6 +15,10 @@ ASM_SOURCES="jump_all_gas make_all_gas ontop_all_gas"
 CXX_SOURCE_DIR="src"
 CXX_SOURCES="context_stack io concurrency"
 
+# tests
+TEST_DIR="tests"
+TEST_CASES="algorithm range"
+
 # output lib
 OSTD_LIB="libostd"
 
@@ -184,6 +188,7 @@ clean() {
     evalv "rm -f \"$OSTD_STATIC_LIB\""
     evalv "rm -f \"$OSTD_SHARED_LIB\""
     evalv "rm -f test_runner.o test_runner"
+    evalv "rm -rf \"${TEST_DIR}\""
 }
 
 # call_cxx input output [shared]
@@ -234,9 +239,28 @@ build_example() {
     rm -f "examples/${1}.o"
 }
 
+# build _test name
+build_test() {
+    cat << EOF > "${TEST_DIR}/${1}.cc"
+#define OSTD_BUILD_TESTS libostd_${1}
+
+#include <ostd/unit_test.hh>
+#include <ostd/${1}.hh>
+#include <ostd/io.hh>
+
+int main() {
+    auto [ succ, fail ] = ostd::test::run();
+    ostd::writeln(succ, " ", fail);
+    return 0;
+}
+EOF
+    call_cxx "${TEST_DIR}/${1}.cc" "${TEST_DIR}/${1}.o"
+    call_ld "${TEST_DIR}/${1}" "${TEST_DIR}/${1}.o" "$OSTD_DEFAULT_LIB"
+    rm -f "${TEST_DIR}/${1}.o"
+}
+
 # build test runner
 build_test_runner() {
-    OSTD_CXXFLAGS="${OSTD_CXXFLAGS} -DOSTD_DEFAULT_LIB='\"${OSTD_DEFAULT_LIB}\"'"
     call_cxx test_runner.cc test_runner.o
     call_ld test_runner test_runner.o "$OSTD_DEFAULT_LIB"
     rm -f test_runner.o
@@ -283,12 +307,6 @@ if [ "$BUILD_SHARED" = "yes" ]; then
 fi
 evalv "rm -f $ASM_OBJ"
 
-# build test runner
-if [ "$BUILD_TESTSUITE" = "yes" ]; then
-    echo "Building test runner..."
-    build_test_runner &
-fi
-
 # build examples
 if [ "$BUILD_EXAMPLES" = "yes" ]; then
     echo "Building examples..."
@@ -297,8 +315,25 @@ if [ "$BUILD_EXAMPLES" = "yes" ]; then
     done
 fi
 
+# build test runner and tests
+if [ "$BUILD_TESTSUITE" = "yes" ]; then
+    echo "Building tests..."
+    build_test_runner &
+    if [ ! -d "$TEST_DIR" ]; then
+        mkdir -p "$TEST_DIR"
+    fi
+    for test in $TEST_CASES; do
+        build_test "$test" &
+    done
+fi
+
 # wait for remaining tasks
 wait
 
+# run tests if meant to
+if [ "$BUILD_TESTSUITE" = "yes" ]; then
+    ./test_runner "$TEST_DIR"
+fi
+
 # done
 exit 0
diff --git a/test_runner.cc b/test_runner.cc
index ba13638..e3003e9 100644
--- a/test_runner.cc
+++ b/test_runner.cc
@@ -1,4 +1,4 @@
-#include <atomic>
+#include <cstddef>
 #include <unordered_map>
 
 #include <ostd/platform.hh>
@@ -7,8 +7,6 @@
 #include <ostd/io.hh>
 #include <ostd/string.hh>
 #include <ostd/filesystem.hh>
-#include <ostd/environ.hh>
-#include <ostd/thread_pool.hh>
 
 using namespace ostd;
 
@@ -27,27 +25,6 @@ constexpr auto COLOR_END = "";
 #define popen _popen
 #endif
 
-#ifndef OSTD_DEFAULT_LIB
-#define OSTD_DEFAULT_LIB "libostd.a"
-#endif
-
-static void write_test_src(file_stream &s, string_range modname) {
-    s.writefln(
-        "#define OSTD_BUILD_TESTS libostd_%s\n"
-        "\n"
-        "#include <ostd/unit_test.hh>\n"
-        "#include <ostd/%s.hh>\n"
-        "#include <ostd/io.hh>\n"
-        "\n"
-        "int main() {\n"
-        "    auto [ succ, fail ] = ostd::test::run();\n"
-        "    ostd::writeln(succ, \" \", fail);\n"
-        "    return 0;\n"
-        "}",
-        modname, modname
-    );
-}
-
 static void write_padded(string_range s, std::size_t n) {
     write(s, "...");
     if ((s.size() + 3) >= n) {
@@ -58,107 +35,72 @@ static void write_padded(string_range s, std::size_t n) {
     }
 }
 
-int main() {
+int main(int argc, char **argv) {
     /* configurable section */
-
-    auto compiler = env_get("CXX").value_or("c++");
-    auto cxxflags = "-std=c++1z -I. -Wall -Wextra -Wshadow -Wold-style-cast "
-                    "-Wno-missing-braces"; /* clang false positive */
-
-    auto userflags = env_get("CXXFLAGS").value_or("");
+    char const *testdir = "tests";
+    if (argc > 1) {
+        testdir = argv[1];
+    }
 
     /* do not change past this point */
 
-    std::atomic_int nsuccess = 0, nfailed = 0;
+    std::size_t nsuccess = 0, nfailed = 0;
 
-    auto print_error = [&](string_range modname, string_range fmsg) {
+    auto print_error = [&](string_range modname) {
         write_padded(modname, 20);
-        writeln(COLOR_RED, COLOR_BOLD, '(', fmsg, ')', COLOR_END);
+        writeln(COLOR_RED, COLOR_BOLD, "(runtime error)", COLOR_END);
         ++nfailed;
     };
 
-    ostd::thread_pool tpool;
-    tpool.start(std::thread::hardware_concurrency());
-
-    filesystem::directory_iterator ds{"ostd"};
+    filesystem::directory_iterator ds{testdir};
     for (auto &v: ds) {
         auto p = filesystem::path{v};
-        if (
-            (!filesystem::is_regular_file(p)) ||
-            (p.extension().string() != ".hh")
-        ) {
+        if (!filesystem::is_regular_file(p)) {
             continue;
         }
-        tpool.push([&, modname = p.stem().string()]() {
 #ifdef OSTD_PLATFORM_WIN32
-            std::string exepath = ".\\test_";
-            exepath += modname;
-            exepath += ".exe";
+        if (p.extension().string() != ".exe")
 #else
-            std::string exepath = "./test_";
-            exepath += modname;
+        if (p.extension().string() != "")
 #endif
+        {
+            continue;
+        }
+        auto modname = p.stem().string();
+        auto exepath = p.string();
 
-            auto cxxcmd = appender<std::string>();
-            format(cxxcmd, "%s -o %s %s", compiler, exepath, cxxflags);
-            if (!userflags.empty()) {
-                cxxcmd.get() += ' ';
-                cxxcmd.get() += userflags;
-            }
-            cxxcmd.get() += " -xc++ - -xnone ";
-            cxxcmd.get() += OSTD_DEFAULT_LIB;
+        auto rf = popen(exepath.data(), "r");
+        if (!rf) {
+            print_error(modname);
+            continue;
+        }
 
-            /* compile */
-            auto cf = popen(cxxcmd.get().data(), "w");
-            if (!cf) {
-                print_error(modname, "compile errror");
-                return;
-            }
+        int succ = 0, fail = 0;
+        if (fscanf(rf, "%d %d", &succ, &fail) != 2) {
+            pclose(rf);
+            print_error(modname);
+            continue;
+        }
 
-            file_stream cfs{cf};
-            write_test_src(cfs, modname);
+        if (pclose(rf)) {
+            print_error(modname);
+            continue;
+        }
 
-            if (pclose(cf)) {
-                print_error(modname, "compile errror");
-                return;
-            }
+        write_padded(modname, 20);
+        writefln(
+            "%s%s%d out of %d%s (%d failures)",
+            fail ? COLOR_RED : COLOR_GREEN, COLOR_BOLD,
+            succ, succ + fail, COLOR_END, fail
+        );
 
-            /* run */
-            auto rf = popen(exepath.data(), "r");
-            if (!rf) {
-                print_error(modname, "runtime error");
-                return;
-            }
-
-            int succ = 0, fail = 0;
-            if (fscanf(rf, "%d %d", &succ, &fail) != 2) {
-                print_error(modname, "runtime error");
-            }
-
-            if (pclose(rf)) {
-                print_error(modname, "runtime error");
-                return;
-            }
-
-            write_padded(modname, 20);
-            writefln(
-                "%s%s%d out of %d%s (%d failures)",
-                fail ? COLOR_RED : COLOR_GREEN, COLOR_BOLD,
-                succ, succ + fail, COLOR_END, fail
-            );
-
-            remove(exepath.data());
-            if (fail) {
-                ++nfailed;
-            } else {
-                ++nsuccess;
-            }
-        });
+        if (fail) {
+            ++nfailed;
+        } else {
+            ++nsuccess;
+        }
     }
 
-    /* wait for tasks */
-    tpool.destroy();
-
     writeln("\n", COLOR_BLUE, COLOR_BOLD, "testing done:", COLOR_END);
     writeln(COLOR_GREEN, "SUCCESS: ", int(nsuccess), COLOR_END);
     writeln(COLOR_RED, "FAILURE: ", int(nfailed), COLOR_END);