diff --git a/src/osmo_gsm_tester/core/trial.py b/src/osmo_gsm_tester/core/trial.py
new file mode 100644
index 0000000..83b0f11
--- /dev/null
+++ b/src/osmo_gsm_tester/core/trial.py
@@ -0,0 +1,213 @@
+# osmo_gsm_tester: trial: directory of binaries to be tested
+#
+# Copyright (C) 2016-2017 by sysmocom - s.f.m.c. GmbH
+#
+# Author: Neels Hofmeyr <neels@hofmeyr.de>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import os
+import time
+import shutil
+import tarfile
+
+from . import log
+from . import util
+from . import report
+from . import suite
+
+FILE_MARK_TAKEN = 'taken'
+FILE_CHECKSUMS = 'checksums.md5'
+TIMESTAMP_FMT = '%Y-%m-%d_%H-%M-%S'
+FILE_LAST_RUN = 'last_run'
+FILE_LOG = 'log'
+FILE_LOG_BRIEF = 'log_brief'
+
+class Trial(log.Origin):
+    UNKNOWN = 'UNKNOWN'
+    PASS = 'PASS'
+    FAIL = 'FAIL'
+
+    @staticmethod
+    def next(trials_dir):
+
+        with trials_dir.lock('Trial.next'):
+            trials = [e for e in trials_dir.children()
+                      if trials_dir.isdir(e) and not trials_dir.exists(e, FILE_MARK_TAKEN)]
+            if not trials:
+                return None
+            # sort by time to get the one that waited longest
+            trials.sort(key=lambda e: os.path.getmtime(trials_dir.child(e)))
+            next_trial = trials[0]
+            return Trial(trials_dir.child(next_trial)).take()
+
+    def __init__(self, trial_dir):
+        self.path = os.path.abspath(trial_dir)
+        super().__init__(log.C_TST, os.path.basename(self.path))
+        self.dir = util.Dir(self.path)
+        self.inst_dir = util.Dir(self.dir.child('inst'))
+        self.bin_tars = []
+        self.suites = []
+        self.status = Trial.UNKNOWN
+        self._run_dir = None
+        self.log_targets = None
+
+    def __repr__(self):
+        return self.name()
+
+    def __enter__(self):
+        '''add a log target to log to the run dir, write taken marker, log a
+        starting separator.'''
+        run_dir = self.get_run_dir()
+        detailed_log = run_dir.new_child(FILE_LOG)
+        self.log_targets = [
+            log.FileLogTarget(detailed_log)
+              .set_all_levels(log.L_DBG)
+              .style_change(trace=True),
+            log.FileLogTarget(run_dir.new_child(FILE_LOG_BRIEF))
+              .style_change(src=False, all_origins_on_levels=(log.L_ERR, log.L_TRACEBACK))
+            ]
+        log.large_separator(self.name(), sublevel=1)
+        self.log('Detailed log at', detailed_log)
+        self.take()
+        return self
+
+    def __exit__(self, *exc_info):
+        '''log a report, then remove log file targets for this trial'''
+        self.log_report()
+        for lt in self.log_targets:
+            lt.remove()
+        self.log_targets = None
+
+    def take(self):
+        self.dir.touch(FILE_MARK_TAKEN)
+        return self
+
+    def get_run_dir(self):
+        if self._run_dir is not None:
+            return self._run_dir
+        self._run_dir = util.Dir(self.dir.new_child('run.%s' % time.strftime(TIMESTAMP_FMT)))
+        self._run_dir.mkdir()
+
+        last_run = self.dir.child(FILE_LAST_RUN)
+        if os.path.islink(last_run):
+            os.remove(last_run)
+        if not os.path.exists(last_run):
+            os.symlink(self.dir.rel_path(self._run_dir.path), last_run)
+        return self._run_dir
+
+    def verify(self):
+        "verify checksums"
+
+        if not self.dir.exists():
+            raise RuntimeError('Trial dir does not exist: %r' % self.dir)
+        if not self.dir.isdir():
+            raise RuntimeError('Trial dir is not a dir: %r' % self.dir)
+
+        checksums = self.dir.child(FILE_CHECKSUMS)
+        if not self.dir.isfile(FILE_CHECKSUMS):
+            raise RuntimeError('No checksums file in trial dir: %r', checksums)
+
+        with open(checksums, 'r') as f:
+            line_nr = 0
+            for line in [l.strip() for l in f.readlines()]:
+                line_nr += 1
+                if not line:
+                    continue
+                md5, filename = line.split('  ')
+                file_path = self.dir.child(filename)
+
+                if not self.dir.isfile(filename):
+                    raise RuntimeError('File listed in checksums file but missing in trials dir:'
+                                       ' %r vs. %r line %d' % (file_path, checksums, line_nr))
+
+                if md5 != util.md5_of_file(file_path):
+                    raise RuntimeError('Checksum mismatch for %r vs. %r line %d'
+                                       % (file_path, checksums, line_nr))
+
+                if filename.endswith('.tgz'):
+                    self.bin_tars.append(filename)
+
+    def has_bin_tar(self, bin_name):
+        bin_tar_start = '%s.' % bin_name
+        matches = [t for t in self.bin_tars if t.startswith(bin_tar_start)]
+        self.dbg(bin_name=bin_name, matches=matches)
+        if not matches:
+            return None
+        if len(matches) > 1:
+            raise RuntimeError('More than one match for bin name %r: %r' % (bin_name, matches))
+        bin_tar = matches[0]
+        bin_tar_path = self.dir.child(bin_tar)
+        if not os.path.isfile(bin_tar_path):
+            raise RuntimeError('Not a file or missing: %r' % bin_tar_path)
+        return bin_tar_path
+
+    def get_inst(self, bin_name):
+        bin_tar = self.has_bin_tar(bin_name)
+        if not bin_tar:
+            raise RuntimeError('No such binary available: %r' % bin_name)
+        inst_dir = self.inst_dir.child(bin_name)
+
+        if os.path.isdir(inst_dir):
+            # already unpacked
+            return inst_dir
+
+        t = None
+        try:
+            os.makedirs(inst_dir)
+            t = tarfile.open(bin_tar)
+            t.extractall(inst_dir)
+            return inst_dir
+
+        except:
+            shutil.rmtree(inst_dir)
+            raise
+        finally:
+            if t:
+                try:
+                    t.close()
+                except:
+                    pass
+
+    def add_suite_run(self, suite_scenario_str, suite_def, scenarios):
+        suite_run = suite.SuiteRun(self, suite_scenario_str, suite_def, scenarios)
+        self.suites.append(suite_run)
+
+    def run_suites(self, names=None):
+        self.status = Trial.UNKNOWN
+        try:
+            for suite_run in self.suites:
+                try:
+                    suite_run.run_tests(names)
+                except BaseException as e:
+                    # when the program is aborted by a signal (like Ctrl-C), escalate to abort all.
+                    self.err('TRIAL RUN ABORTED: %s' % type(e).__name__)
+                    # log the traceback before the trial's logging is ended
+                    log.log_exn()
+                    raise
+                finally:
+                    if suite_run.status != suite.SuiteRun.PASS:
+                        self.status = Trial.FAIL
+            if self.status == Trial.UNKNOWN:
+                self.status = Trial.PASS
+        finally:
+            junit_path = self.get_run_dir().new_file(self.name()+'.xml')
+            self.log('Storing JUnit report in', junit_path)
+            report.trial_to_junit_write(self, junit_path)
+
+    def log_report(self):
+        log.large_separator(self.name(), self.status)
+        self.log(report.trial_to_text(self))
+
+# vim: expandtab tabstop=4 shiftwidth=4