diff --git a/beast/unit_test/amount.h b/beast/unit_test/amount.h
index ef95014045..25db44411f 100644
--- a/beast/unit_test/amount.h
+++ b/beast/unit_test/amount.h
@@ -31,28 +31,36 @@ namespace unit_test {
 class amount
 {
 private:
-    std::size_t n;
-    std::string const& what;
+    std::size_t n_;
+    std::string const& what_;
 
 public:
     amount (amount const&) = default;
     amount& operator= (amount const&) = delete;
 
-    amount (std::size_t n_, std::string const& what_)
-        : n (n_)
-        , what (what_)
-    {
-    }
+    template <class = void>
+    amount (std::size_t n, std::string const& what);
 
     friend
     std::ostream&
-    operator<< (std::ostream& s, amount const& t)
-    {
-        s << t.n << " " << t.what << ((t.n != 1) ? "s" : "");
-        return s;
-    }
+    operator<< (std::ostream& s, amount const& t);
 };
 
+template <class>
+amount::amount (std::size_t n, std::string const& what)
+    : n_ (n)
+    , what_ (what)
+{
+}
+
+inline
+std::ostream&
+operator<< (std::ostream& s, amount const& t)
+{
+    s << t.n_ << " " << t.what_ << ((t.n_ != 1) ? "s" : "");
+    return s;
+}
+
 } // unit_test
 } // beast
 
diff --git a/beast/unit_test/define_print.cpp b/beast/unit_test/define_print.cpp
index 00194879fc..27e2c2d7a7 100644
--- a/beast/unit_test/define_print.cpp
+++ b/beast/unit_test/define_print.cpp
@@ -20,58 +20,79 @@
 #include <beast/unit_test/amount.h>
 #include <beast/unit_test/global_suites.h>
 #include <beast/unit_test/suite.h>
+#include <string>
 
 // Include this .cpp in your project to gain access to the printing suite
 
 namespace beast {
 namespace unit_test {
-
 namespace detail {
 
 /** A suite that prints the list of globally defined suites. */
 class print_test : public suite
 {
+private:
+    template <class = void>
+    void
+    do_run();
+
 public:
+    template <class = void>
     static
     std::string
-    prefix (suite_info const& s)
-    {
-        if (s.manual())
-            return "|M| ";
-        return "    ";
-    }
+    prefix (suite_info const& s);
 
+    template <class = void>
     void
-    print (suite_list &c)
-    {
-        std::size_t manual (0);
-        for (auto const& s : c)
-        {
-            log <<
-                prefix (s) <<
-                s.full_name();
-            if (s.manual())
-                ++manual;
-        }
-        log <<
-            amount (c.size(), "suite") << " total, " <<
-            amount (manual, "manual suite")
-            ;
-    }
+    print (suite_list &c);
 
     void
     run()
     {
-        log << "------------------------------------------";
-        print (global_suites());
-        log << "------------------------------------------";
-        pass();
+        do_run();
     }
 };
 
+template <class>
+void
+print_test::do_run()
+{
+    log << "------------------------------------------";
+    print (global_suites());
+    log << "------------------------------------------";
+    pass();
+}
+
+template <class>
+std::string
+print_test::prefix (suite_info const& s)
+{
+    if (s.manual())
+        return "|M| ";
+    return "    ";
+}
+
+template <class>
+void
+print_test::print (suite_list &c)
+{
+    std::size_t manual (0);
+    for (auto const& s : c)
+    {
+        log <<
+            prefix (s) <<
+            s.full_name();
+        if (s.manual())
+            ++manual;
+    }
+    log <<
+        amount (c.size(), "suite") << " total, " <<
+        amount (manual, "manual suite")
+        ;
+}
+
 BEAST_DEFINE_TESTSUITE_MANUAL(print,unit_test,beast);
 
 }
-
 }
 }
diff --git a/beast/unit_test/global_suites.h b/beast/unit_test/global_suites.h
index eb61b9b62e..8a446c91ed 100644
--- a/beast/unit_test/global_suites.h
+++ b/beast/unit_test/global_suites.h
@@ -27,8 +27,7 @@ namespace unit_test {
 
 namespace detail {
 
-// Non const container is a detail, users are not allowed to modify!
-inline
+template <class = void>
 suite_list&
 global_suites()
 {
@@ -36,18 +35,23 @@ global_suites()
     return s;
 }
 
-// Used to insert suites during static initialization
 template <class Suite>
-struct global_suite_instance
+struct insert_suite
 {
-    global_suite_instance (char const* name, char const* module,
-        char const* library, bool manual)
-    {
-        global_suites().insert <Suite> (
-            name, module, library, manual);
-    }
+    template <class = void>
+    insert_suite (char const* name, char const* module,
+        char const* library, bool manual);
 };
 
+template <class Suite>
+template <class>
+insert_suite<Suite>::insert_suite (char const* name,
+    char const* module, char const* library, bool manual)
+{
+    global_suites().insert <Suite> (
+        name, module, library, manual);
+}
+
 } // detail
 
 /** Holds suites registered during static initialization. */
@@ -58,7 +62,7 @@ global_suites()
     return detail::global_suites();
 }
 
-} // unit_test
-} // beast
+}
+}
 
 #endif
diff --git a/beast/unit_test/match.h b/beast/unit_test/match.h
index 763c1ac655..6b6cf96e87 100644
--- a/beast/unit_test/match.h
+++ b/beast/unit_test/match.h
@@ -56,69 +56,80 @@ private:
     std::string m_library;
 
 public:
+    template <class = void>
     explicit
-    selector (mode_t mode, std::string const& pattern = "")
-        : m_mode (mode)
-        , m_pat (pattern)
-    {
-        if (m_mode == automatch && pattern.empty())
-            m_mode = all;
-    }
+    selector (mode_t mode, std::string const& pattern = "");
 
+    template <class = void>
     bool
-    operator() (suite_info const& s)
-    {
-        switch (m_mode)
-        {
-        case automatch:
-            // check suite
-            if (m_pat == s.name())
-            {
-                m_mode = none;
-                return true;
-            }
-
-            // check module
-            if (m_pat == s.module())
-            {
-                m_mode = module;
-                m_library = s.library();
-                return ! s.manual();
-            }
-
-            // check library
-            if (m_pat == s.library())
-            {
-                m_mode = library;
-                return ! s.manual();
-            }
-
-            return false;
-
-        case suite:
-            return m_pat == s.name();
-
-        case module:
-            return m_pat == s.module() && ! s.manual();
-
-        case library:
-            return m_pat == s.library() && ! s.manual();
-
-        case none:
-            return false;
-
-        case all:
-        default:
-            // fall through
-            break;
-        };
-
-        return ! s.manual();
-    }
+    operator() (suite_info const& s);
 };
 
 //------------------------------------------------------------------------------
 
+template <class>
+selector::selector (mode_t mode, std::string const& pattern)
+    : m_mode (mode)
+    , m_pat (pattern)
+{
+    if (m_mode == automatch && pattern.empty())
+        m_mode = all;
+}
+
+template <class>
+bool
+selector::operator() (suite_info const& s)
+{
+    switch (m_mode)
+    {
+    case automatch:
+        // check suite
+        if (m_pat == s.name())
+        {
+            m_mode = none;
+            return true;
+        }
+
+        // check module
+        if (m_pat == s.module())
+        {
+            m_mode = module;
+            m_library = s.library();
+            return ! s.manual();
+        }
+
+        // check library
+        if (m_pat == s.library())
+        {
+            m_mode = library;
+            return ! s.manual();
+        }
+
+        return false;
+
+    case suite:
+        return m_pat == s.name();
+
+    case module:
+        return m_pat == s.module() && ! s.manual();
+
+    case library:
+        return m_pat == s.library() && ! s.manual();
+
+    case none:
+        return false;
+
+    case all:
+    default:
+        // fall through
+        break;
+    };
+
+    return ! s.manual();
+}
+
+//------------------------------------------------------------------------------
+
 // Utility functions for producing predicates to select suites.
 
 /** Returns a predicate that implements a smart matching rule.
diff --git a/beast/unit_test/results.h b/beast/unit_test/results.h
index d19687d080..0e4ee1e5fe 100644
--- a/beast/unit_test/results.h
+++ b/beast/unit_test/results.h
@@ -55,11 +55,11 @@ private:
         : public const_container <std::vector <test>>
     {
     private:
-        std::size_t m_failed;
+        std::size_t failed_;
 
     public:
         tests_t ()
-            : m_failed (0)
+            : failed_ (0)
         {
         }
 
@@ -74,7 +74,7 @@ private:
         std::size_t
         failed() const
         {
-            return m_failed;
+            return failed_;
         }
 
         /** Register a successful test condition. */
@@ -88,7 +88,7 @@ private:
         void
         fail (std::string const& reason = "")
         {
-            ++m_failed;
+            ++failed_;
             cont().emplace_back (false, reason);
         }
     };
@@ -105,11 +105,11 @@ private:
         }
     };
 
-    std::string m_name;
+    std::string name_;
 
 public:
     explicit case_results (std::string const& name = "")
-        : m_name (name)
+        : name_ (name)
     {
     }
 
@@ -117,7 +117,7 @@ public:
     std::string const&
     name() const
     {
-        return m_name;
+        return name_;
     }
 
     /** Memberspace for a container of test condition outcomes. */
@@ -134,15 +134,13 @@ class suite_results
     : public const_container <std::vector <case_results>>
 {
 private:
-    std::string m_name;
-    std::size_t m_total;
-    std::size_t m_failed;
+    std::string name_;
+    std::size_t total_ = 0;
+    std::size_t failed_ = 0;
 
 public:
     explicit suite_results (std::string const& name = "")
-        : m_name (name)
-        , m_total (0)
-        , m_failed (0)
+        : name_ (name)
     {
     }
 
@@ -150,21 +148,21 @@ public:
     std::string const&
     name() const
     {
-        return m_name;
+        return name_;
     }
 
     /** Returns the total number of test conditions. */
     std::size_t
     total() const
     {
-        return m_total;
+        return total_;
     }
 
     /** Returns the number of failures. */
     std::size_t
     failed() const
     {
-        return m_failed;
+        return failed_;
     }
 
     /** Insert a set of testcase results. */
@@ -173,16 +171,16 @@ public:
     insert (case_results&& r)
     {
         cont().emplace_back (std::move (r));
-        m_total += r.tests.total();
-        m_failed += r.tests.failed();
+        total_ += r.tests.total();
+        failed_ += r.tests.failed();
     }
 
     void
     insert (case_results const& r)
     {
         cont().push_back (r);
-        m_total += r.tests.total();
-        m_failed += r.tests.failed();
+        total_ += r.tests.total();
+        failed_ += r.tests.failed();
     }
     /** @} */
 };
@@ -196,14 +194,14 @@ class results
 {
 private:
     std::size_t m_cases;
-    std::size_t m_total;
-    std::size_t m_failed;
+    std::size_t total_;
+    std::size_t failed_;
 
 public:
     results()
         : m_cases (0)
-        , m_total (0)
-        , m_failed (0)
+        , total_ (0)
+        , failed_ (0)
     {
     }
 
@@ -218,14 +216,14 @@ public:
     std::size_t
     total() const
     {
-        return m_total;
+        return total_;
     }
 
     /** Returns the number of failures. */
     std::size_t
     failed() const
     {
-        return m_failed;
+        return failed_;
     }
 
     /** Insert a set of suite results. */
@@ -234,8 +232,8 @@ public:
     insert (suite_results&& r)
     {
         m_cases += r.size();
-        m_total += r.total();
-        m_failed += r.failed();
+        total_ += r.total();
+        failed_ += r.failed();
         cont().emplace_back (std::move (r));
     }
 
@@ -243,8 +241,8 @@ public:
     insert (suite_results const& r)
     {
         m_cases += r.size();
-        m_total += r.total();
-        m_failed += r.failed();
+        total_ += r.total();
+        failed_ += r.failed();
         cont().push_back (r);
     }
     /** @} */
diff --git a/beast/unit_test/runner.h b/beast/unit_test/runner.h
index befd699780..164770f628 100644
--- a/beast/unit_test/runner.h
+++ b/beast/unit_test/runner.h
@@ -21,10 +21,9 @@
 #define BEAST_UNIT_TEST_RUNNER_H_INCLUDED
 
 #include <beast/unit_test/suite_info.h>
-
 #include <beast/streams/abstract_ostream.h>
-
 #include <cassert>
+#include <mutex>
 #include <string>
 
 namespace beast {
@@ -47,22 +46,22 @@ private:
         stream_t() = delete;
         stream_t& operator= (stream_t const&) = delete;
 
-        stream_t (runner& owner)
-            : owner_ (owner)
-        {
-        }
+        template <class = void>
+        stream_t (runner& owner);
 
         void
-        write (string_type const& s)
+        write (string_type const& s) override
         {
             owner_.log (s);
         }
     };
 
     stream_t stream_;
-    bool default_;
-    bool failed_;
-    bool cond_;
+    std::string arg_;
+    bool default_ = false;
+    bool failed_ = false;
+    bool cond_ = false;
+    std::recursive_mutex mutex_;
 
 public:
     virtual ~runner() = default;
@@ -72,6 +71,25 @@ public:
     template <class = void>
     runner();
 
+    /** Set the argument string.
+        The argument string is available to suites and
+        allows for customization of the test. Each suite
+        defines its own syntax for the argumnet string.
+        The same argument is passed to all suites.
+    */
+    void
+    arg (std::string const& s)
+    {
+        arg_ = s;
+    }
+
+    /** Returns the argument string. */
+    std::string const&
+    arg() const
+    {
+        return arg_;
+    }
+
     /** Run the specified suite.
         @return `true` if any conditions failed.
     */
@@ -201,12 +219,17 @@ private:
 
 //------------------------------------------------------------------------------
 
+template <class>
+runner::stream_t::stream_t (runner& owner)
+    : owner_ (owner)
+{
+}
+
+//------------------------------------------------------------------------------
+
 template <class>
 runner::runner()
     : stream_ (*this)
-    , default_ (false)
-    , failed_ (false)
-    , cond_ (false)
 {
 }
 
@@ -272,6 +295,7 @@ template <class>
 void
 runner::testcase (std::string const& name)
 {
+    std::lock_guard<std::recursive_mutex> lock(mutex_);
     // Name may not be empty
     assert (default_ || ! name.empty());
     // Forgot to call pass or fail
@@ -287,6 +311,7 @@ template <class>
 void
 runner::pass()
 {
+    std::lock_guard<std::recursive_mutex> lock(mutex_);
     if (default_)
         testcase ("");
     on_pass();
@@ -297,6 +322,7 @@ template <class>
 void
 runner::fail (std::string const& reason)
 {
+    std::lock_guard<std::recursive_mutex> lock(mutex_);
     if (default_)
         testcase ("");
     on_fail (reason);
@@ -308,6 +334,7 @@ template <class>
 void
 runner::log (std::string const& s)
 {
+    std::lock_guard<std::recursive_mutex> lock(mutex_);
     if (default_)
         testcase ("");
     on_log (s);
diff --git a/beast/unit_test/suite.h b/beast/unit_test/suite.h
index 9254ba30f9..b9c4f7d657 100644
--- a/beast/unit_test/suite.h
+++ b/beast/unit_test/suite.h
@@ -166,6 +166,13 @@ public:
     bool
     expect (Condition shouldBeTrue, std::string const& reason = "");
 
+    /** Return the argument associated with the runner. */
+    std::string const&
+    arg() const
+    {
+        return runner_->arg();
+    }
+
     // DEPRECATED
     // @return `true` if the test condition indicates success (a false value)
     template <class Condition>
@@ -398,8 +405,8 @@ suite::fail (std::string const& reason)
 // detail:
 // This inserts the suite with the given manual flag
 #define BEAST_DEFINE_TESTSUITE_INSERT(Class,Module,Library,manual) \
-    static beast::unit_test::detail::global_suite_instance <Class##_test>    \
-        Library ## Module ## Class ## _test_instance (                       \
+    static beast::unit_test::detail::insert_suite <Class##_test>   \
+        Library ## Module ## Class ## _test_instance (             \
             #Class, #Module, #Library, manual);
 
 //------------------------------------------------------------------------------