diff --git a/ostd/environ.hh b/ostd/environ.hh
new file mode 100644
index 0000000..0493d87
--- /dev/null
+++ b/ostd/environ.hh
@@ -0,0 +1,62 @@
+/* Environment handling.
+ *
+ * This file is part of OctaSTD. See COPYING.md for futher information.
+ */
+
+#ifndef OSTD_ENVIRON_HH
+#define OSTD_ENVIRON_HH
+
+#include <stdlib.h>
+#include <string.h>
+
+#include "ostd/maybe.hh"
+#include "ostd/string.hh"
+
+namespace ostd {
+namespace environ {
+
+inline Maybe<ConstCharRange> get(ConstCharRange name) {
+    char buf[256];
+    const char *ret = nullptr;
+    if (name.size() < sizeof(buf)) {
+        memcpy(buf, name.data(), name.size());
+        buf[name.size()] = '\0';
+        ret = getenv(buf);
+    } else {
+        ret = getenv(String(name).data());
+    }
+    if (!ret) return ostd::nothing;
+    return ostd::move(ConstCharRange(ret));
+}
+
+inline bool set(ConstCharRange name, ConstCharRange value,
+                bool update = true) {
+    char sbuf[2048];
+    char *buf = sbuf;
+    bool alloc = (name.size() + value.size() + 2) > sizeof(sbuf);
+    if (alloc)
+        buf = new char[name.size() + value.size() + 2];
+    memcpy(buf, name.data(), name.size());
+    buf[name.size()] = '\0';
+    memcpy(&buf[name.size() + 1], value.data(), value.size());
+    buf[name.size() + value.size() + 1] = '\0';
+    bool ret = !setenv(buf, &buf[name.size() + 1], update);
+    if (alloc)
+        delete[] buf;
+    return ret;
+}
+
+inline bool unset(ConstCharRange name) {
+    char buf[256];
+    if (name.size() < sizeof(buf)) {
+        memcpy(buf, name.data(), name.size());
+        buf[name.size()] = '\0';
+        return !unsetenv(buf);
+    }
+    return !unsetenv(String(name).data());
+}
+
+} /* namespace environ */
+} /* namespace ostd */
+
+#endif
diff --git a/test_runner.cc b/test_runner.cc
index 14f49f7..2812962 100644
--- a/test_runner.cc
+++ b/test_runner.cc
@@ -1,102 +1,90 @@
-#include <stdio.h>
-#include <stdlib.h>
-
 #include <ostd/platform.hh>
 #include <ostd/io.hh>
 #include <ostd/string.hh>
 #include <ostd/map.hh>
 #include <ostd/filesystem.hh>
+#include <ostd/environ.hh>
 
 using namespace ostd;
 
-ConstCharRange get_env(ConstCharRange var, ConstCharRange def = nullptr) {
-    const char *ret = getenv(String(var).data());
-    if (!ret || !ret[0])
-        return def;
-    return ret;
-}
+#ifndef OSTD_PLATFORM_WIN32
+constexpr auto ColorRed = "\033[91m";
+constexpr auto ColorGreen = "\033[92m";
+constexpr auto ColorBlue = "\033[94m";
+constexpr auto ColorBold = "\033[1m";
+constexpr auto ColorEnd = "\033[0m";
+#else
+constexpr auto ColorRed = "";
+constexpr auto ColorGreen = "";
+constexpr auto ColorBlue = "";
+constexpr auto ColorBold = "";
+constexpr auto ColorEnd = "";
+#endif
 
 int main() {
-    ConstCharRange compiler = get_env("CXX", "c++");
-    ConstCharRange cxxflags = "-std=c++14 -Wall -Wextra -Wshadow "
-                              "-Wno-missing-braces " /* clang false positive */
-                              "-I.";
-    ConstCharRange testdir = get_env("TESTDIR", "tests");
-    ConstCharRange srcext = ".cc";
+    /* configurable section */
 
-    Map<ConstCharRange, ConstCharRange> colors = {
-#ifndef OSTD_PLATFORM_WIN32
-        { "red", "\033[91m" },
-        { "green", "\033[92m" },
-        { "blue", "\033[94m" },
-        { "bold", "\033[1m" },
-        { "end", "\033[0m" }
-#else
-        { "red", "" },
-        { "green", "" },
-        { "blue", "" },
-        { "bold", "" },
-        { "end", "" }
-#endif
-    };
+    auto compiler = environ::get("CXX").value_or("c++");
+    auto cxxflags = "-std=c++14 -Wall -Wextra -Wshadow "
+                    "-Wno-missing-braces " /* clang false positive */
+                    "-I.";
+    auto testdir = environ::get("TESTDIR").value_or("tests");
+    auto srcext = ".cc";
+
+    auto userflags = environ::get("CXXFLAGS").value_or("");
+
+    /* do not change past this point */
 
-    ConstCharRange userflags = get_env("CXXFLAGS", "");
     int nsuccess = 0, nfailed = 0;
+    ConstCharRange modname = nullptr;
 
-    auto print_result = [&colors, &nsuccess, &nfailed]
-                        (ConstCharRange modname, ConstCharRange fmsg = nullptr) {
+    auto print_result = [&](ConstCharRange fmsg = nullptr) {
         write(modname, "...\t");
         if (!fmsg.empty()) {
-            writeln(colors["red"], colors["bold"], "(", fmsg, ")", colors["end"]);
+            writeln(ColorRed, ColorBold, "(", fmsg, ")", ColorEnd);
             ++nfailed;
         } else {
-            writeln(colors["green"], colors["bold"], "(success)", colors["end"]);
+            writeln(ColorGreen, ColorBold, "(success)", ColorEnd);
             ++nsuccess;
         }
     };
 
     DirectoryStream ds(testdir);
     for (auto v: ds.iter()) {
-        if (v.type() != FileType::regular)
-            continue;
-        if (v.extension() != srcext)
+        if ((v.type() != FileType::regular) || (v.extension() != srcext))
             continue;
 
+        modname = v.stem();
+
         String exepath = testdir;
         exepath += PathSeparator;
-        exepath += v.stem();
+        exepath += modname;
 
-        String cxxcmd = compiler;
-        cxxcmd += " ";
-        cxxcmd += testdir;
-        cxxcmd += PathSeparator;
-        cxxcmd += v.filename();
-        cxxcmd += " -o ";
-        cxxcmd += exepath;
-        cxxcmd += " ";
-        cxxcmd += cxxflags;
+        auto cxxcmd = appender<String>();
+        format(cxxcmd, "%s %s%s%s -o %s %s", compiler, testdir, PathSeparator,
+               v.filename(), exepath, cxxflags);
         if (!userflags.empty()) {
-            cxxcmd += " ";
-            cxxcmd += userflags;
+            cxxcmd.get() += " ";
+            cxxcmd.get() += userflags;
         }
 
-        int ret = system(cxxcmd.data());
+        int ret = system(cxxcmd.get().data());
         if (ret) {
-            print_result(v.stem(), "compile errror");
+            print_result("compile errror");
             continue;
         }
 
         ret = system(exepath.data());
         if (ret) {
-            print_result(v.stem(), "runtime error");
+            print_result("runtime error");
             continue;
         }
 
         remove(exepath.data());
-        print_result(v.stem());
+        print_result();
     }
 
-    writeln("\n", colors["blue"], colors["bold"], "testing done:", colors["end"]);
-    writeln(colors["green"], "SUCCESS: ", nsuccess, colors["end"]);
-    writeln(colors["red"], "FAILURE: ", nfailed, colors["end"]);
+    writeln("\n", ColorBlue, ColorBold, "testing done:", ColorEnd);
+    writeln(ColorGreen, "SUCCESS: ", nsuccess, ColorEnd);
+    writeln(ColorRed, "FAILURE: ", nfailed, ColorEnd);
 }