Merge branch 'feature/tests'

11 files changed, 1077 insertions, 38 deletions

diff --git a/.gitignore b/.gitignore
index 42d82d8..07d68cf 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,7 +9,8 @@
 /autom4te.cache/
 /configure
 /config.h.in
-/build-aux/
+/build-aux/*
+!/build-aux/tap-driver.sh
 /ChangeLog
 /INSTALL
 Makefile.in
@@ -27,6 +28,7 @@ Makefile
 *.o
 /version.c
 /@
+/test-suite.log
 /atsign-*.tar*
 /atsign-*/
 /MD5SUMS
diff --git a/Makefile.am b/Makefile.am
index ecdbc4c..103bad8 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -112,3 +112,4 @@ release:
 		files@files.pehjota.net:files/pub/$(PACKAGE)/$(VERSION)/
 
 include $(top_srcdir)/src/local.mk
+include $(top_srcdir)/tests/local.mk
diff --git a/build-aux/tap-driver.sh b/build-aux/tap-driver.sh
new file mode 100644
index 0000000..bc7b1cc
--- /dev/null
+++ b/build-aux/tap-driver.sh
@@ -0,0 +1,651 @@
+#! /bin/sh
+# Copyright (C) 2011-2022 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+# As a special exception to the GNU General Public License, if you
+# distribute this file as part of a program that contains a
+# configuration script generated by Autoconf, you may include it under
+# the same distribution terms that you use for the rest of that program.
+
+# This file is maintained in Automake, please report
+# bugs to <bug-automake@gnu.org> or send patches to
+# <automake-patches@gnu.org>.
+
+scriptversion=2013-12-23.17; # UTC
+
+# Make unconditional expansion of undefined variables an error.  This
+# helps a lot in preventing typo-related bugs.
+set -u
+
+me=tap-driver.sh
+
+fatal ()
+{
+  echo "$me: fatal: $*" >&2
+  exit 1
+}
+
+usage_error ()
+{
+  echo "$me: $*" >&2
+  print_usage >&2
+  exit 2
+}
+
+print_usage ()
+{
+  cat <<END
+Usage:
+  tap-driver.sh --test-name=NAME --log-file=PATH --trs-file=PATH
+                [--expect-failure={yes|no}] [--color-tests={yes|no}]
+                [--enable-hard-errors={yes|no}] [--ignore-exit]
+                [--diagnostic-string=STRING] [--merge|--no-merge]
+                [--comments|--no-comments] [--] TEST-COMMAND
+The '--test-name', '-log-file' and '--trs-file' options are mandatory.
+END
+}
+
+# TODO: better error handling in option parsing (in particular, ensure
+# TODO: $log_file, $trs_file and $test_name are defined).
+test_name= # Used for reporting.
+log_file=  # Where to save the result and output of the test script.
+trs_file=  # Where to save the metadata of the test run.
+expect_failure=0
+color_tests=0
+merge=0
+ignore_exit=0
+comments=0
+diag_string='#'
+while test $# -gt 0; do
+  case $1 in
+  --help) print_usage; exit $?;;
+  --version) echo "$me $scriptversion"; exit $?;;
+  --test-name) test_name=$2; shift;;
+  --log-file) log_file=$2; shift;;
+  --trs-file) trs_file=$2; shift;;
+  --color-tests) color_tests=$2; shift;;
+  --expect-failure) expect_failure=$2; shift;;
+  --enable-hard-errors) shift;; # No-op.
+  --merge) merge=1;;
+  --no-merge) merge=0;;
+  --ignore-exit) ignore_exit=1;;
+  --comments) comments=1;;
+  --no-comments) comments=0;;
+  --diagnostic-string) diag_string=$2; shift;;
+  --) shift; break;;
+  -*) usage_error "invalid option: '$1'";;
+  esac
+  shift
+done
+
+test $# -gt 0 || usage_error "missing test command"
+
+case $expect_failure in
+  yes) expect_failure=1;;
+    *) expect_failure=0;;
+esac
+
+if test $color_tests = yes; then
+  init_colors='
+    color_map["red"]="" # Red.
+    color_map["grn"]="" # Green.
+    color_map["lgn"]="" # Light green.
+    color_map["blu"]="" # Blue.
+    color_map["mgn"]="" # Magenta.
+    color_map["std"]=""     # No color.
+    color_for_result["ERROR"] = "mgn"
+    color_for_result["PASS"]  = "grn"
+    color_for_result["XPASS"] = "red"
+    color_for_result["FAIL"]  = "red"
+    color_for_result["XFAIL"] = "lgn"
+    color_for_result["SKIP"]  = "blu"'
+else
+  init_colors=''
+fi
+
+# :; is there to work around a bug in bash 3.2 (and earlier) which
+# does not always set '$?' properly on redirection failure.
+# See the Autoconf manual for more details.
+:;{
+  (
+    # Ignore common signals (in this subshell only!), to avoid potential
+    # problems with Korn shells.  Some Korn shells are known to propagate
+    # to themselves signals that have killed a child process they were
+    # waiting for; this is done at least for SIGINT (and usually only for
+    # it, in truth).  Without the `trap' below, such a behaviour could
+    # cause a premature exit in the current subshell, e.g., in case the
+    # test command it runs gets terminated by a SIGINT.  Thus, the awk
+    # script we are piping into would never seen the exit status it
+    # expects on its last input line (which is displayed below by the
+    # last `echo $?' statement), and would thus die reporting an internal
+    # error.
+    # For more information, see the Autoconf manual and the threads:
+    # <https://lists.gnu.org/archive/html/bug-autoconf/2011-09/msg00004.html>
+    # <http://mail.opensolaris.org/pipermail/ksh93-integration-discuss/2009-February/004121.html>
+    trap : 1 3 2 13 15
+    if test $merge -gt 0; then
+      exec 2>&1
+    else
+      exec 2>&3
+    fi
+    "$@"
+    echo $?
+  ) | LC_ALL=C ${AM_TAP_AWK-awk} \
+        -v me="$me" \
+        -v test_script_name="$test_name" \
+        -v log_file="$log_file" \
+        -v trs_file="$trs_file" \
+        -v expect_failure="$expect_failure" \
+        -v merge="$merge" \
+        -v ignore_exit="$ignore_exit" \
+        -v comments="$comments" \
+        -v diag_string="$diag_string" \
+'
+# TODO: the usages of "cat >&3" below could be optimized when using
+#       GNU awk, and/on on systems that supports /dev/fd/.
+
+# Implementation note: in what follows, `result_obj` will be an
+# associative array that (partly) simulates a TAP result object
+# from the `TAP::Parser` perl module.
+
+## ----------- ##
+##  FUNCTIONS  ##
+## ----------- ##
+
+function fatal(msg)
+{
+  print me ": " msg | "cat >&2"
+  exit 1
+}
+
+function abort(where)
+{
+  fatal("internal error " where)
+}
+
+# Convert a boolean to a "yes"/"no" string.
+function yn(bool)
+{
+  return bool ? "yes" : "no";
+}
+
+function add_test_result(result)
+{
+  if (!test_results_index)
+    test_results_index = 0
+  test_results_list[test_results_index] = result
+  test_results_index += 1
+  test_results_seen[result] = 1;
+}
+
+# Whether the test script should be re-run by "make recheck".
+function must_recheck()
+{
+  for (k in test_results_seen)
+    if (k != "XFAIL" && k != "PASS" && k != "SKIP")
+      return 1
+  return 0
+}
+
+# Whether the content of the log file associated to this test should
+# be copied into the "global" test-suite.log.
+function copy_in_global_log()
+{
+  for (k in test_results_seen)
+    if (k != "PASS")
+      return 1
+  return 0
+}
+
+function get_global_test_result()
+{
+    if ("ERROR" in test_results_seen)
+      return "ERROR"
+    if ("FAIL" in test_results_seen || "XPASS" in test_results_seen)
+      return "FAIL"
+    all_skipped = 1
+    for (k in test_results_seen)
+      if (k != "SKIP")
+        all_skipped = 0
+    if (all_skipped)
+      return "SKIP"
+    return "PASS";
+}
+
+function stringify_result_obj(result_obj)
+{
+  if (result_obj["is_unplanned"] || result_obj["number"] != testno)
+    return "ERROR"
+
+  if (plan_seen == LATE_PLAN)
+    return "ERROR"
+
+  if (result_obj["directive"] == "TODO")
+    return result_obj["is_ok"] ? "XPASS" : "XFAIL"
+
+  if (result_obj["directive"] == "SKIP")
+    return result_obj["is_ok"] ? "SKIP" : COOKED_FAIL;
+
+  if (length(result_obj["directive"]))
+      abort("in function stringify_result_obj()")
+
+  return result_obj["is_ok"] ? COOKED_PASS : COOKED_FAIL
+}
+
+function decorate_result(result)
+{
+  color_name = color_for_result[result]
+  if (color_name)
+    return color_map[color_name] "" result "" color_map["std"]
+  # If we are not using colorized output, or if we do not know how
+  # to colorize the given result, we should return it unchanged.
+  return result
+}
+
+function report(result, details)
+{
+  if (result ~ /^(X?(PASS|FAIL)|SKIP|ERROR)/)
+    {
+      msg = ": " test_script_name
+      add_test_result(result)
+    }
+  else if (result == "#")
+    {
+      msg = " " test_script_name ":"
+    }
+  else
+    {
+      abort("in function report()")
+    }
+  if (length(details))
+    msg = msg " " details
+  # Output on console might be colorized.
+  print decorate_result(result) msg
+  # Log the result in the log file too, to help debugging (this is
+  # especially true when said result is a TAP error or "Bail out!").
+  print result msg | "cat >&3";
+}
+
+function testsuite_error(error_message)
+{
+  report("ERROR", "- " error_message)
+}
+
+function handle_tap_result()
+{
+  details = result_obj["number"];
+  if (length(result_obj["description"]))
+    details = details " " result_obj["description"]
+
+  if (plan_seen == LATE_PLAN)
+    {
+      details = details " # AFTER LATE PLAN";
+    }
+  else if (result_obj["is_unplanned"])
+    {
+       details = details " # UNPLANNED";
+    }
+  else if (result_obj["number"] != testno)
+    {
+       details = sprintf("%s # OUT-OF-ORDER (expecting %d)",
+                         details, testno);
+    }
+  else if (result_obj["directive"])
+    {
+      details = details " # " result_obj["directive"];
+      if (length(result_obj["explanation"]))
+        details = details " " result_obj["explanation"]
+    }
+
+  report(stringify_result_obj(result_obj), details)
+}
+
+# `skip_reason` should be empty whenever planned > 0.
+function handle_tap_plan(planned, skip_reason)
+{
+  planned += 0 # Avoid getting confused if, say, `planned` is "00"
+  if (length(skip_reason) && planned > 0)
+    abort("in function handle_tap_plan()")
+  if (plan_seen)
+    {
+      # Error, only one plan per stream is acceptable.
+      testsuite_error("multiple test plans")
+      return;
+    }
+  planned_tests = planned
+  # The TAP plan can come before or after *all* the TAP results; we speak
+  # respectively of an "early" or a "late" plan.  If we see the plan line
+  # after at least one TAP result has been seen, assume we have a late
+  # plan; in this case, any further test result seen after the plan will
+  # be flagged as an error.
+  plan_seen = (testno >= 1 ? LATE_PLAN : EARLY_PLAN)
+  # If testno > 0, we have an error ("too many tests run") that will be
+  # automatically dealt with later, so do not worry about it here.  If
+  # $plan_seen is true, we have an error due to a repeated plan, and that
+  # has already been dealt with above.  Otherwise, we have a valid "plan
+  # with SKIP" specification, and should report it as a particular kind
+  # of SKIP result.
+  if (planned == 0 && testno == 0)
+    {
+      if (length(skip_reason))
+        skip_reason = "- "  skip_reason;
+      report("SKIP", skip_reason);
+    }
+}
+
+function extract_tap_comment(line)
+{
+  if (index(line, diag_string) == 1)
+    {
+      # Strip leading `diag_string` from `line`.
+      line = substr(line, length(diag_string) + 1)
+      # And strip any leading and trailing whitespace left.
+      sub("^[ \t]*", "", line)
+      sub("[ \t]*$", "", line)
+      # Return what is left (if any).
+      return line;
+    }
+  return "";
+}
+
+# When this function is called, we know that line is a TAP result line,
+# so that it matches the (perl) RE "^(not )?ok\b".
+function setup_result_obj(line)
+{
+  # Get the result, and remove it from the line.
+  result_obj["is_ok"] = (substr(line, 1, 2) == "ok" ? 1 : 0)
+  sub("^(not )?ok[ \t]*", "", line)
+
+  # If the result has an explicit number, get it and strip it; otherwise,
+  # automatically assign the next test number to it.
+  if (line ~ /^[0-9]+$/ || line ~ /^[0-9]+[^a-zA-Z0-9_]/)
+    {
+      match(line, "^[0-9]+")
+      # The final `+ 0` is to normalize numbers with leading zeros.
+      result_obj["number"] = substr(line, 1, RLENGTH) + 0
+      line = substr(line, RLENGTH + 1)
+    }
+  else
+    {
+      result_obj["number"] = testno
+    }
+
+  if (plan_seen == LATE_PLAN)
+    # No further test results are acceptable after a "late" TAP plan
+    # has been seen.
+    result_obj["is_unplanned"] = 1
+  else if (plan_seen && testno > planned_tests)
+    result_obj["is_unplanned"] = 1
+  else
+    result_obj["is_unplanned"] = 0
+
+  # Strip trailing and leading whitespace.
+  sub("^[ \t]*", "", line)
+  sub("[ \t]*$", "", line)
+
+  # This will have to be corrected if we have a "TODO"/"SKIP" directive.
+  result_obj["description"] = line
+  result_obj["directive"] = ""
+  result_obj["explanation"] = ""
+
+  if (index(line, "#") == 0)
+    return # No possible directive, nothing more to do.
+
+  # Directives are case-insensitive.
+  rx = "[ \t]*#[ \t]*([tT][oO][dD][oO]|[sS][kK][iI][pP])[ \t]*"
+
+  # See whether we have the directive, and if yes, where.
+  pos = match(line, rx "$")
+  if (!pos)
+    pos = match(line, rx "[^a-zA-Z0-9_]")
+
+  # If there was no TAP directive, we have nothing more to do.
+  if (!pos)
+    return
+
+  # Let`s now see if the TAP directive has been escaped.  For example:
+  #  escaped:     ok \# SKIP
+  #  not escaped: ok \\# SKIP
+  #  escaped:     ok \\\\\# SKIP
+  #  not escaped: ok \ # SKIP
+  if (substr(line, pos, 1) == "#")
+    {
+      bslash_count = 0
+      for (i = pos; i > 1 && substr(line, i - 1, 1) == "\\"; i--)
+        bslash_count += 1
+      if (bslash_count % 2)
+        return # Directive was escaped.
+    }
+
+  # Strip the directive and its explanation (if any) from the test
+  # description.
+  result_obj["description"] = substr(line, 1, pos - 1)
+  # Now remove the test description from the line, that has been dealt
+  # with already.
+  line = substr(line, pos)
+  # Strip the directive, and save its value (normalized to upper case).
+  sub("^[ \t]*#[ \t]*", "", line)
+  result_obj["directive"] = toupper(substr(line, 1, 4))
+  line = substr(line, 5)
+  # Now get the explanation for the directive (if any), with leading
+  # and trailing whitespace removed.
+  sub("^[ \t]*", "", line)
+  sub("[ \t]*$", "", line)
+  result_obj["explanation"] = line
+}
+
+function get_test_exit_message(status)
+{
+  if (status == 0)
+    return ""
+  if (status !~ /^[1-9][0-9]*$/)
+    abort("getting exit status")
+  if (status < 127)
+    exit_details = ""
+  else if (status == 127)
+    exit_details = " (command not found?)"
+  else if (status >= 128 && status <= 255)
+    exit_details = sprintf(" (terminated by signal %d?)", status - 128)
+  else if (status > 256 && status <= 384)
+    # We used to report an "abnormal termination" here, but some Korn
+    # shells, when a child process die due to signal number n, can leave
+    # in $? an exit status of 256+n instead of the more standard 128+n.
+    # Apparently, both behaviours are allowed by POSIX (2008), so be
+    # prepared to handle them both.  See also Austing Group report ID
+    # 0000051 <http://www.austingroupbugs.net/view.php?id=51>
+    exit_details = sprintf(" (terminated by signal %d?)", status - 256)
+  else
+    # Never seen in practice.
+    exit_details = " (abnormal termination)"
+  return sprintf("exited with status %d%s", status, exit_details)
+}
+
+function write_test_results()
+{
+  print ":global-test-result: " get_global_test_result() > trs_file
+  print ":recheck: "  yn(must_recheck()) > trs_file
+  print ":copy-in-global-log: " yn(copy_in_global_log()) > trs_file
+  for (i = 0; i < test_results_index; i += 1)
+    print ":test-result: " test_results_list[i] > trs_file
+  close(trs_file);
+}
+
+BEGIN {
+
+## ------- ##
+##  SETUP  ##
+## ------- ##
+
+'"$init_colors"'
+
+# Properly initialized once the TAP plan is seen.
+planned_tests = 0
+
+COOKED_PASS = expect_failure ? "XPASS": "PASS";
+COOKED_FAIL = expect_failure ? "XFAIL": "FAIL";
+
+# Enumeration-like constants to remember which kind of plan (if any)
+# has been seen.  It is important that NO_PLAN evaluates "false" as
+# a boolean.
+NO_PLAN = 0
+EARLY_PLAN = 1
+LATE_PLAN = 2
+
+testno = 0     # Number of test results seen so far.
+bailed_out = 0 # Whether a "Bail out!" directive has been seen.
+
+# Whether the TAP plan has been seen or not, and if yes, which kind
+# it is ("early" is seen before any test result, "late" otherwise).
+plan_seen = NO_PLAN
+
+## --------- ##
+##  PARSING  ##
+## --------- ##
+
+is_first_read = 1
+
+while (1)
+  {
+    # Involutions required so that we are able to read the exit status
+    # from the last input line.
+    st = getline
+    if (st < 0) # I/O error.
+      fatal("I/O error while reading from input stream")
+    else if (st == 0) # End-of-input
+      {
+        if (is_first_read)
+          abort("in input loop: only one input line")
+        break
+      }
+    if (is_first_read)
+      {
+        is_first_read = 0
+        nextline = $0
+        continue
+      }
+    else
+      {
+        curline = nextline
+        nextline = $0
+        $0 = curline
+      }
+    # Copy any input line verbatim into the log file.
+    print | "cat >&3"
+    # Parsing of TAP input should stop after a "Bail out!" directive.
+    if (bailed_out)
+      continue
+
+    # TAP test result.
+    if ($0 ~ /^(not )?ok$/ || $0 ~ /^(not )?ok[^a-zA-Z0-9_]/)
+      {
+        testno += 1
+        setup_result_obj($0)
+        handle_tap_result()
+      }
+    # TAP plan (normal or "SKIP" without explanation).
+    else if ($0 ~ /^1\.\.[0-9]+[ \t]*$/)
+      {
+        # The next two lines will put the number of planned tests in $0.
+        sub("^1\\.\\.", "")
+        sub("[^0-9]*$", "")
+        handle_tap_plan($0, "")
+        continue
+      }
+    # TAP "SKIP" plan, with an explanation.
+    else if ($0 ~ /^1\.\.0+[ \t]*#/)
+      {
+        # The next lines will put the skip explanation in $0, stripping
+        # any leading and trailing whitespace.  This is a little more
+        # tricky in truth, since we want to also strip a potential leading
+        # "SKIP" string from the message.
+        sub("^[^#]*#[ \t]*(SKIP[: \t][ \t]*)?", "")
+        sub("[ \t]*$", "");
+        handle_tap_plan(0, $0)
+      }
+    # "Bail out!" magic.
+    # Older versions of prove and TAP::Harness (e.g., 3.17) did not
+    # recognize a "Bail out!" directive when preceded by leading
+    # whitespace, but more modern versions (e.g., 3.23) do.  So we
+    # emulate the latter, "more modern" behaviour.
+    else if ($0 ~ /^[ \t]*Bail out!/)
+      {
+        bailed_out = 1
+        # Get the bailout message (if any), with leading and trailing
+        # whitespace stripped.  The message remains stored in `$0`.
+        sub("^[ \t]*Bail out![ \t]*", "");
+        sub("[ \t]*$", "");
+        # Format the error message for the
+        bailout_message = "Bail out!"
+        if (length($0))
+          bailout_message = bailout_message " " $0
+        testsuite_error(bailout_message)
+      }
+    # Maybe we have too look for dianogtic comments too.
+    else if (comments != 0)
+      {
+        comment = extract_tap_comment($0);
+        if (length(comment))
+          report("#", comment);
+      }
+  }
+
+## -------- ##
+##  FINISH  ##
+## -------- ##
+
+# A "Bail out!" directive should cause us to ignore any following TAP
+# error, as well as a non-zero exit status from the TAP producer.
+if (!bailed_out)
+  {
+    if (!plan_seen)
+      {
+        testsuite_error("missing test plan")
+      }
+    else if (planned_tests != testno)
+      {
+        bad_amount = testno > planned_tests ? "many" : "few"
+        testsuite_error(sprintf("too %s tests run (expected %d, got %d)",
+                                bad_amount, planned_tests, testno))
+      }
+    if (!ignore_exit)
+      {
+        # Fetch exit status from the last line.
+        exit_message = get_test_exit_message(nextline)
+        if (exit_message)
+          testsuite_error(exit_message)
+      }
+  }
+
+write_test_results()
+
+exit 0
+
+} # End of "BEGIN" block.
+'
+
+# TODO: document that we consume the file descriptor 3 :-(
+} 3>"$log_file"
+
+test $? -eq 0 || fatal "I/O or internal error"
+
+# Local Variables:
+# mode: shell-script
+# sh-indentation: 2
+# eval: (add-hook 'before-save-hook 'time-stamp)
+# time-stamp-start: "scriptversion="
+# time-stamp-format: "%:y-%02m-%02d.%02H"
+# time-stamp-time-zone: "UTC0"
+# time-stamp-end: "; # UTC"
+# End:
diff --git a/configure.ac b/configure.ac
index 7c94fbd..011b7d5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -40,7 +40,7 @@ AC_CHECK_FUNCS(
 	[\
 		calloc difftime fprintf fputs free isspace localtime mktime \
 		printf realloc setvbuf sleep strerror strlen strftime strptime \
-		time
+		time timegm
 	],
 	[],
 	[funcs_missing=true])
diff --git a/src/datetime.c b/src/datetime.c
index 7c5dcfa..230a348 100644
--- a/src/datetime.c
+++ b/src/datetime.c
@@ -116,19 +116,15 @@ _datetime_reset_tm(struct tm *tm)
 }
 
 static void
-_datetime_normalize(struct tm *arg_tm, time_t *arg_sec)
+_datetime_normalize(struct tm *now_tm, struct tm *arg_tm, time_t *arg_sec)
 {
-	time_t     now_sec;
-	struct tm *now_tm;
-	int        wday;
+	int wday;
 
 	if (arg_tm->tm_sec == INT_MIN) {
 		arg_tm->tm_sec = 0;
 	}
 	if (arg_tm->tm_mday == INT_MIN && arg_tm->tm_wday == INT_MIN) {
 		/* No date specified; try today. */
-		now_sec = time(NULL);
-		now_tm = localtime(&now_sec);
 		arg_tm->tm_year = now_tm->tm_year;
 		arg_tm->tm_mon  = now_tm->tm_mon;
 		arg_tm->tm_mday = now_tm->tm_mday;
@@ -150,8 +146,6 @@ _datetime_normalize(struct tm *arg_tm, time_t *arg_sec)
 		/* Only a weekday specified; try tomorrow or next week.  Uses
 		 * same shortcut as above. */
 		wday = arg_tm->tm_wday;
-		now_sec = time(NULL);
-		now_tm = localtime(&now_sec);
 		arg_tm->tm_year = now_tm->tm_year;
 		arg_tm->tm_mon  = now_tm->tm_mon;
 		arg_tm->tm_mday = now_tm->tm_mday;
@@ -163,8 +157,6 @@ _datetime_normalize(struct tm *arg_tm, time_t *arg_sec)
 		*arg_sec += (60 * 60 * 24) * (wday - now_tm->tm_wday);
 	} else if (arg_tm->tm_year == INT_MIN) {
 		/* No year specified; try this year. */
-		now_sec = time(NULL);
-		now_tm = localtime(&now_sec);
 		arg_tm->tm_year = now_tm->tm_year;
 		*arg_sec = mktime(arg_tm);
 		if (*arg_sec <= mktime(now_tm)) {
@@ -179,7 +171,7 @@ _datetime_normalize(struct tm *arg_tm, time_t *arg_sec)
 }
 
 int
-datetime_parse(const char *input, time_t *arg_sec)
+datetime_parse(struct tm *now_tm, const char *input, time_t *arg_sec)
 {
 	int        date_fmt_len;
 	int        time_fmt_len;
@@ -219,7 +211,7 @@ datetime_parse(const char *input, time_t *arg_sec)
 			end = strptime(input, fmt_buf, &arg_tm);
 			if (end != NULL && *end == '\0') {
 				free(fmt_buf);
-				_datetime_normalize(&arg_tm, arg_sec);
+				_datetime_normalize(now_tm, &arg_tm, arg_sec);
 				return 0;
 			}
 		}
@@ -235,7 +227,7 @@ datetime_parse(const char *input, time_t *arg_sec)
 			end = strptime(input, fmt_buf, &arg_tm);
 			if (end != NULL && *end == '\0') {
 				free(fmt_buf);
-				_datetime_normalize(&arg_tm, arg_sec);
+				_datetime_normalize(now_tm, &arg_tm, arg_sec);
 				return 0;
 			}
 		}
@@ -246,7 +238,7 @@ datetime_parse(const char *input, time_t *arg_sec)
 		end = strptime(input, DATETIME_MISC_FMTS_[d], &arg_tm);
 		if (end != NULL && *end == '\0') {
 			free(fmt_buf);
-			_datetime_normalize(&arg_tm, arg_sec);
+			_datetime_normalize(now_tm, &arg_tm, arg_sec);
 			return 0;
 		}
 	}
diff --git a/src/datetime.h b/src/datetime.h
index edff8f7..554748b 100644
--- a/src/datetime.h
+++ b/src/datetime.h
@@ -23,7 +23,7 @@
 #include <time.h>
 
 int
-datetime_parse(const char *input, time_t *arg_sec);
+datetime_parse(struct tm *now_tm, const char *input, time_t *arg_sec);
 
 int
 datetime_strftime_date(const struct tm *tm, char **out, size_t *out_sz,
diff --git a/src/main.c b/src/main.c
index bb4abb5..ff6c15c 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2021  P. J. McDermott
+ * Copyright (C) 2021, 2022  P. J. McDermott
  *
  * This file is part of @
  *
@@ -18,6 +18,7 @@
  */
 
 #include <errno.h>
+#include <inttypes.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -56,6 +57,18 @@ static const struct option LONGOPTS_[] = {
 };
 #endif
 
+static struct tm EPOCH_ = {
+	.tm_sec   = 0,
+	.tm_min   = 0,
+	.tm_hour  = 0,
+	.tm_mday  = 1,
+	.tm_mon   = 0,
+	.tm_year  = 70,
+	.tm_wday  = 4,
+	.tm_yday  = 0,
+	.tm_isdst = -1,
+};
+
 static void
 _print_usage(FILE *stream, const char *program_name)
 {
@@ -78,18 +91,52 @@ _print_help(const char *program_name)
 #endif
 }
 
-static void
-_list_formats(void)
+static struct tm *
+_set_now(char buf[])
 {
-	time_t     tim;
-	struct tm *tm;
-	char      *out;
-	size_t     buf_sz;
-	char      *buf;
-	size_t     i;
+	struct tm  tm;
+	char      *endptr;
+	time_t     t;
+	struct tm *tm_p;
 
-	tim = time(NULL);
-	tm  = localtime(&tim);
+	if (strlen(buf) != 19) {
+		return NULL;
+	}
+	if (buf[4] != '-' || buf[7] != '-' || buf[10] != ' ' ||
+			buf[13] != ':' || buf[16] != ':') {
+		return NULL;
+	}
+	buf[4] = '\0', buf[7] = '\0', buf[10] = '\0';
+	buf[13] = '\0', buf[16] = '\0';
+	tm.tm_sec   = strtol(buf + 17, &endptr, 10);
+	if (endptr[0] != '\0') { return NULL; }
+	tm.tm_min   = strtol(buf + 14, &endptr, 10);
+	if (endptr[0] != '\0') { return NULL; }
+	tm.tm_hour  = strtol(buf + 11, &endptr, 10);
+	if (endptr[0] != '\0') { return NULL; }
+	tm.tm_mday  = strtol(buf +  8, &endptr, 10);
+	if (endptr[0] != '\0') { return NULL; }
+	tm.tm_mon   = strtol(buf +  5, &endptr, 10) -    1;
+	if (endptr[0] != '\0') { return NULL; }
+	tm.tm_year  = strtol(buf +  0, &endptr, 10) - 1900;
+	if (endptr[0] != '\0') { return NULL; }
+	tm.tm_wday  = -1;
+	tm.tm_yday  = -1;
+	tm.tm_isdst = -1;
+
+	t = mktime(&tm);
+	tm_p = localtime(&t);
+
+	return tm_p;
+}
+
+static void
+_list_formats(const struct tm *tm)
+{
+	char   *out;
+	size_t  buf_sz;
+	char   *buf;
+	size_t  i;
 
 	puts("Time formats:");
 	i = 0;
@@ -168,29 +215,41 @@ _concat_args(int argc, char * const argv[])
 int
 main(int argc, char * const argv[])
 {
-	int     opt;
-	char   *buf;
-	time_t  arg;
-	time_t  now;
-	double  dif;
+	bool       dbg;
+	bool       fmt;
+	int        opt;
+	char      *buf;
+	time_t     now;
+	struct tm *now_tm;
+	time_t     arg;
+	double     dif;
 
+	dbg = false;
+	fmt = false;
 	optind = 1;
 	opterr = 0;
 #if defined(HAVE_GETOPT_LONG) && HAVE_GETOPT_LONG
-	while ((opt = getopt_long(argc, argv, "FhV", LONGOPTS_, NULL)) > 0) {
+	while ((opt = getopt_long(argc, argv, "FhVd:", LONGOPTS_, NULL)) > 0) {
 #else
-	while ((opt = getopt(argc, argv, "FhV")) > 0) {
+	while ((opt = getopt(argc, argv, "FhVd:")) > 0) {
 #endif
 		switch (opt) {
 			case 'F':
-				_list_formats();
-				return EXIT_SUCCESS;
+				fmt = true;
+				break;
 			case 'h':
 				_print_help(argv[0]);
 				return EXIT_SUCCESS;
 			case 'V':
 				_print_version();
 				return EXIT_SUCCESS;
+			case 'd':
+				dbg = true;
+				now_tm = _set_now(optarg);
+				if (now_tm == NULL) {
+					return EXIT_FAILURE;
+				}
+				break;
 			default:
 				_print_usage(stderr, argv[0]);
 #if defined(HAVE_GETOPT_LONG) && HAVE_GETOPT_LONG
@@ -206,17 +265,34 @@ main(int argc, char * const argv[])
 	argc -= optind;
 	argv += optind;
 
+	if (dbg == false) {
+		now = time(NULL);
+		now_tm = localtime(&now);
+	}
+
+	if (fmt == true) {
+		_list_formats(now_tm);
+		return EXIT_SUCCESS;
+	}
+
 	buf = _concat_args(argc, argv);
 	if (buf == NULL) {
 		return EXIT_FAILURE;
 	}
 
-	if (datetime_parse(buf, &arg) < 0) {
+	if (datetime_parse(now_tm, buf, &arg) < 0) {
 		free(buf);
 		return EXIT_FAILURE;
 	}
 	free(buf);
 
+	if (dbg == true) {
+		now = timegm(&EPOCH_);
+		dif = difftime(arg, now);
+		printf("%" PRId64 "\n", (int64_t) dif);
+		return EXIT_SUCCESS;
+	}
+
 	time(&now);
 	dif = difftime(arg, now);
 	if (dif >= 1000 * 24 * 60 * 60) {
diff --git a/tests/.gitignore b/tests/.gitignore
new file mode 100644
index 0000000..7e563b8
--- /dev/null
+++ b/tests/.gitignore
@@ -0,0 +1,2 @@
+*.log
+*.trs
diff --git a/tests/aux/tap-functions.sh b/tests/aux/tap-functions.sh
new file mode 100644
index 0000000..e2414b7
--- /dev/null
+++ b/tests/aux/tap-functions.sh
@@ -0,0 +1,229 @@
+# -*- shell-script -*-
+#
+# Copyright (C) 2011-2022 Free Software Foundation, Inc.
+#
+# 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 2, 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 <https://www.gnu.org/licenses/>.
+
+# Helper functions used by TAP-producing tests of the Automake testsuite.
+
+#
+# IMPORTANT: All the functions defined in this file can *not* be used
+#            from within a subshell, unless explicitly noted otherwise.
+#
+
+# The counts of the TAP test results seen so far: total count and
+# per-result counts.
+tap_count_=0
+tap_pass_count_=0
+tap_skip_count_=0
+tap_fail_count_=0
+tap_xfail_count_=0
+tap_xpass_count_=0
+
+# not COMMAND [ARGS...]
+# ---------------------
+# Run the given command and invert its exit status.
+not () { ! "$@"; }
+
+# plan_ [unknown|later|lazy|now|NUMBER-OF-PLANNED-TESTS]
+# ------------------------------------------------------
+# Print a TAP plan for the given number of tests.  This must be called
+# before reporting any test result.  If called with the special argument
+# "unknown" or "later", it will do nothing, expecting the calling script
+# to declare the plan later.  If called with the special argument "lazy"
+# or "now", it will print a TAP plan that accounts for the number of tests
+# seen so far.
+plan_ ()
+{
+  if test $# -eq 0; then
+    bailout_ "plan_: missing argument"
+  elif test $# -ge 2; then
+    bailout_ "plan_: too many arguments"
+  elif test x"$planned_" != x"none" && test x"$planned_" != x"later"; then
+    bailout_ "plan_: called to many times"
+  elif test x"$1" = x"unknown" || test x"$1" = x"later"; then
+    # This means we want to get back later to declaring the TAP plan.
+    planned_=later
+    return 0
+  elif test x"$1" = x"lazy" || test x"$1" = x"now"; then
+    planned_=$tap_count_ # Number of test results seen so far.
+  elif test $1 -ge 0; then
+    planned_=$1
+  else
+    bailout_ "plan_: invalid argument '$1'"
+  fi
+  echo "1..$planned_"
+}
+planned_=none
+
+# diag_ [EXPLANATION]
+# ------------------
+# Report the given text as TAP diagnostic.  Assumes the string denoting
+# TAP diagnostic lines is stored in the '$diag_string_' variable; this is
+# done to allow better interplay with TAP drivers that allow such a string
+# to be configured.
+diag_ ()
+{
+  test $# -eq 0 || echo "$diag_string_ $*"
+}
+
+# Used by the 'diag_' function above.  User-overridable.
+diag_string_="#"
+
+# warn_ [EXPLANATION]
+# ------------------
+# Give a warning (using TAP diagnostic).
+warn_ ()
+{
+  case $# in
+    0) diag_ "WARNING: (unknown warning)";;
+    *) diag_ "WARNING: $*";;
+  esac
+}
+
+# result_ RESULT [-D DIRECTIVE] [-r REASON] [--] [DESCRIPTION...]
+# ---------------------------------------------------------------
+# Report a test case with the given RESULT (valid values are "ok" and
+# "not ok") and the given DESCRIPTION (if any).  If DIRECTIVE is given
+# and non-empty (valid values being "TODO" and "SKIP"), it will be
+# reported too, with the REASON (if given) appended.
+result_ ()
+{
+  test $# -gt 0 || bailout_ "result_: missing argument"
+  tap_result_=$1; shift
+  case $tap_result_ in
+    "ok"|"not ok") ;;
+    *) bailout_ "result_: invalid result '$tap_result'" ;;
+  esac
+  tap_directive_= tap_reason_=
+  while test $# -gt 0; do
+    case $1 in
+      -D|--directive) tap_directive_=$2; shift;;
+      -r|--reason) tap_reason_=$2; shift;;
+      --) shift; break;;
+      -*) bailout_ "result_: invalid option '$1'";;
+       *) break;;
+    esac
+    shift
+  done
+  case $tap_directive_ in
+    ""|TODO|SKIP) ;;
+    *) bailout_ "result_: invalid directive '$directive_'" ;;
+  esac
+  tap_count_=$(($tap_count_ + 1))
+  case $tap_result_,$tap_directive_ in
+    ok,)                                                # Passed.
+      tap_pass_count_=$(($tap_pass_count_ + 1))         ;;
+    not\ ok,TODO)                                       # Expected failure.
+      tap_xfail_count_=$(($tap_xfail_count_ + 1))       ;;
+    not\ ok,*)                                          # Failed.
+      tap_fail_count_=$(($tap_fail_count_ + 1))         ;;
+    ok,TODO)                                            # Unexpected pass.
+      tap_xpass_count_=$(($tap_xpass_count_ + 1))       ;;
+    ok,SKIP)                                            # Skipped.
+      tap_skip_count_=$(($tap_skip_count_ + 1))         ;;
+    *)                                                  # Can't happen.
+      bailout_ "internal error in 'result_'"            ;;
+  esac
+  tap_text_="$tap_result_ $tap_count_"
+  if test x"$*" != x; then
+    tap_text_="$tap_text_ - $*"
+  fi
+  if test x"$tap_directive_" != x; then
+    tap_text_="$tap_text_ # $tap_directive_"${tap_reason_:+" $tap_reason_"}
+  fi
+  printf '%s\n' "$tap_text_"
+}
+
+#  Shorthands for common usages of 'result_'.
+ok_ () { result_ 'ok' ${1+"$@"}; }
+not_ok_ () { result_ 'not ok' ${1+"$@"}; }
+skip_ () { result_ 'ok' -D SKIP ${1+"$@"}; }
+
+# skip_row_ COUNT [-r REASON] [--] [DESCRIPTION...]
+# -------------------------------------------------
+# Report a COUNT of skipped test, with the given reason and descriptions
+# (if any).  Useful to avoid cascade failures in case a fair number of
+# tests depend on an earlier one that failed.
+skip_row_ ()
+{
+  skip_count_=$1; shift
+  for i_ in $(seq_ $skip_count_); do skip_ ${1+"$@"}; done
+}
+
+# skip_all_ [REASON ...]
+# ----------------------
+# Skip all the tests in a test script.  Must be used before calling 'plan_'
+# or reporting any test result.  Can't be used from within a subshell.
+skip_all_ ()
+{
+  echo "1..0 # SKIP" ${1+"$@"}
+  planned_=0
+  exit 0
+}
+
+# bailout_ [REASON ...]
+# ---------------------
+# Stop the execution of the current test suite right now, due to an
+# unrecoverable error.  Can be called at any point, but cannot be used
+# from within a subshell.
+bailout_ ()
+{
+  echo 'Bail out!' ${1+"$@"}
+  exit 99
+}
+
+# fatal_ [REASON ...]
+# -------------------
+# Same as 'bailout_'; for compatibility with 'plain-functions.sh'.
+fatal_ ()
+{
+  bailout_ ${1+"$@"}
+}
+
+# framework_failure_ [REASON ...]
+# -------------------------------
+# Stop the execution of the current test suite right now, due to an
+# unrecoverable error in the set-up of the test case.  Can be called
+# at any point, but cannot be used from within a subshell.
+framework_failure_ ()
+{
+  bailout_ "set-up failure"${1+": $*"}
+}
+
+# command_ok_ TEST-DESCRIPTION [OPTIONS..] [--] CMD [ARGS...]
+# -----------------------------------------------------------
+# Helper subroutine for when a TAP result must be determined by the
+# outcome of a command.
+command_ok_ ()
+{
+  tap_directive_= tap_reason_=
+  test $# -gt 0 || bailout_ "command_ok_: missing argument"
+  tap_description_=$1; shift
+  while test $# -gt 0; do
+    case $1 in
+      -D|--directive) tap_directive_=$2; shift;;
+      -r|--reason) tap_reason_=$2; shift;;
+      --) shift; break;;
+      -*) bailout_ "command_ok_: invalid option '$1'";;
+       *) break;;
+    esac
+    shift
+  done
+  tap_result_="ok"; "$@" || tap_result_="not ok"
+  result_ "$tap_result_" -D "$tap_directive_" -r "$tap_reason_" \
+          -- "$tap_description_"
+}
+
+:
diff --git a/tests/local.mk b/tests/local.mk
new file mode 100644
index 0000000..95671bc
--- /dev/null
+++ b/tests/local.mk
@@ -0,0 +1,13 @@
+TESTS = \
+	%reldir%/parse.sh
+TEST_EXTENSIONS = .sh
+SH_LOG_DRIVER = \
+	AM_TAP_AWK='$(AWK)' \
+	TOP_SRCDIR="$(abs_top_srcdir)" \
+	TOP_BUILDDIR="$(abs_top_builddir)" \
+	$(SHELL) $(top_srcdir)/build-aux/tap-driver.sh
+EXTRA_DIST += \
+	$(TESTS) \
+	$(top_srcdir)/build-aux/tap-driver.sh \
+	%reldir%/aux/tap-functions.sh \
+	%reldir%/parse.sh
diff --git a/tests/parse.sh b/tests/parse.sh
new file mode 100755
index 0000000..1150f28
--- /dev/null
+++ b/tests/parse.sh
@@ -0,0 +1,73 @@
+# Tests @'s date/time parsing
+#
+# Copyright (C) 2022  P. J. McDermott
+#
+# This file is part of @
+#
+# @ is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# @ is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with @.  If not, see <http://www.gnu.org/licenses/>.
+
+set -eu
+
+. "${TOP_SRCDIR}/tests/aux/tap-functions.sh"
+
+fmts="$(TZ=UTC0 "${TOP_BUILDDIR}/@" -d '1970-01-01 00:00:00' -F)"
+time_fmts="$(printf '%s\n' "${fmts}" | \
+	sed -n '/^Time formats:$/,/^Date formats:$/s/^  \* //p')"
+date_fmts="$(printf '%s\n' "${fmts}" | \
+	sed -n '/^Date formats:$/,/^Additional formats:$/s/^  \* //p')"
+misc_fmts="$(printf '%s\n' "${fmts}" | \
+	sed -n '/^Additional formats:$/,$s/^  \* //p')"
+
+plan_ $((\
+	$(printf '%s\n' "${time_fmts}" | wc -l) + \
+	$(printf '%s\n' "${time_fmts}" | wc -l) * \
+	$(printf '%s\n' "${date_fmts}" | wc -l) * \
+	2 + \
+	$(printf '%s\n' "${misc_fmts}" | wc -l) \
+	))
+
+IFS='
+'
+
+for fmt in $(printf '%s\n' "${fmts}"); do
+	diag_ "${fmt}"
+done
+
+run_test()
+{
+	datetime="${1}"
+	shift 1
+
+	got="$(TZ=UTC0 "${TOP_BUILDDIR}/@" -d '1969-12-31 23:59:30' \
+		"${datetime}" 2>&1)" || :
+	if [ x"${got}" = x'0' ]; then
+		ok_ -- "${datetime}"
+	else
+		not_ok_ -- "${datetime}"
+		diag_ " Failed test '${datetime}'"
+		diag_ "         got: '${got}'"
+		diag_ "    expected: '0'"
+	fi
+}
+
+for time_fmt in ${time_fmts}; do
+	run_test "${time_fmt}"
+	for date_fmt in ${date_fmts}; do
+		run_test "${date_fmt} ${time_fmt}"
+		run_test "${time_fmt} ${date_fmt}"
+	done
+done
+for misc_fmt in ${misc_fmts}; do
+	run_test "${misc_fmt}"
+done