Merge bitcoin#16561: tests: Use colors and dots in test_runner.py output only if standard output is a terminal

37f2784 tests: Use colors and dots in test_runner.py output only if standard output is a terminal -- allows for using the test runner output as input to other programs (practicalswift)

Pull request description:

  Use colors and dots in `test_runner.py` output only if standard output is a terminal -- allows for using the test runner output as input to other programs.

  I found the need for this when parsing `test_runner.py` output while investigating intermittent functional test failures.

  Before:

  ```
  $ test/functional/test_runner.py wallet_hd.py > output 2>&1
  $ less output
  Temporary test directory at /tmp/test_runner_₿_🏃_20190807_074115
  ESC[1mWARNING!ESC[0m There is already a bitcoind process running on this system. Tests may fail unexpectedly due to resource contention!
  Remaining jobs: [wallet_hd.py]
  .......................................^M                                       ^M1/1 - ESC[1mwallet_hd.pyESC[0m passed, Duration: 20 s

  ESC[1mTEST         | STATUS    | DURATION

  ESC[0mESC[0;32mwallet_hd.py | ✓ Passed  | 20 s
  ESC[0mESC[1m
  ALL          | ✓ Passed  | 20 s (accumulated)
  ESC[0mRuntime: 20 s
  ```

  After:

  ```
  $ test/functional/test_runner.py wallet_hd.py > output 2>&1
  $ less output
  Temporary test directory at /tmp/test_runner_₿_🏃_20190807_074244
  1/1 - wallet_hd.py passed, Duration: 20 s
  WARNING! There is already a bitcoind process running on this system. Tests may fail unexpectedly due to resource contention!
  Remaining jobs: [wallet_hd.py]

  TEST         | STATUS    | DURATION

  wallet_hd.py | ✓ Passed  | 20 s

  ALL          | ✓ Passed  | 20 s (accumulated)
  Runtime: 20 s
  ```

ACKs for top commit:
  laanwj:
    ACK 37f2784

Tree-SHA512: f15d95f9e07de2954c326d63d7a4bcd2971faeaa00386600dec2fb915ec89475aeef1dbc968b2c12aa5e988d4b3ed1974d6da0b6a3f1e1a105cfd90e8cb97cf6

Author: MarcoFalke

test/functional/test_runner.py

@@ -228,6 +228,7 @@ def main():
                                      epilog='''
     Help text and arguments for individual test script:''',
                                      formatter_class=argparse.RawTextHelpFormatter)
+    parser.add_argument('--ansi', action='store_true', default=sys.stdout.isatty(), help="Use ANSI colors and dots in output (enabled by default when standard output is a TTY)")
     parser.add_argument('--combinedlogslen', '-c', type=int, default=0, metavar='n', help='On failure, print a log (of length n lines) to the console, combined from the test framework and all test nodes.')
     parser.add_argument('--coverage', action='store_true', help='generate a basic coverage report for the RPC interface')
     parser.add_argument('--ci', action='store_true', help='Run checks and code that are usually only enabled in a continuous integration environment')
@@ -240,7 +241,14 @@ def main():
     parser.add_argument('--tmpdirprefix', '-t', default=tempfile.gettempdir(), help="Root directory for datadirs")
     parser.add_argument('--failfast', action='store_true', help='stop execution after the first test failure')
     parser.add_argument('--filter', help='filter scripts to run by regular expression')
+
     args, unknown_args = parser.parse_known_args()
+    if not args.ansi:
+        global BOLD, GREEN, RED, GREY
+        BOLD = ("", "")
+        GREEN = ("", "")
+        RED = ("", "")
+        GREY = ("", "")
 
     # args to be passed on always start with two dashes; tests are the remaining unknown args
     tests = [arg for arg in unknown_args if arg[:2] != "--"]
@@ -342,9 +350,10 @@ def main():
         combined_logs_len=args.combinedlogslen,
         failfast=args.failfast,
         runs_ci=args.ci,
+        use_term_control=args.ansi,
     )
 
-def run_tests(*, test_list, src_dir, build_dir, tmpdir, jobs=1, enable_coverage=False, args=None, combined_logs_len=0, failfast=False, runs_ci):
+def run_tests(*, test_list, src_dir, build_dir, tmpdir, jobs=1, enable_coverage=False, args=None, combined_logs_len=0, failfast=False, runs_ci, use_term_control):
     args = args or []
 
     # Warn if bitcoind is already running (unix only)
@@ -386,6 +395,7 @@ def run_tests(*, test_list, src_dir, build_dir, tmpdir, jobs=1, enable_coverage=
         test_list=test_list,
         flags=flags,
         timeout_duration=40 * 60 if runs_ci else float('inf'),  # in seconds
+        use_term_control=use_term_control,
     )
     start_time = time.time()
     test_results = []
@@ -469,7 +479,7 @@ class TestHandler:
     Trigger the test scripts passed in via the list.
     """
 
-    def __init__(self, *, num_tests_parallel, tests_dir, tmpdir, test_list, flags, timeout_duration):
+    def __init__(self, *, num_tests_parallel, tests_dir, tmpdir, test_list, flags, timeout_duration, use_term_control):
         assert num_tests_parallel >= 1
         self.num_jobs = num_tests_parallel
         self.tests_dir = tests_dir
@@ -479,6 +489,7 @@ def __init__(self, *, num_tests_parallel, tests_dir, tmpdir, test_list, flags, t
         self.flags = flags
         self.num_running = 0
         self.jobs = []
+        self.use_term_control = use_term_control
 
     def get_next(self):
         while self.num_running < self.num_jobs and self.test_list:
@@ -530,11 +541,13 @@ def get_next(self):
                         status = "Failed"
                     self.num_running -= 1
                     self.jobs.remove(job)
-                    clearline = '\r' + (' ' * dot_count) + '\r'
-                    print(clearline, end='', flush=True)
+                    if self.use_term_control:
+                        clearline = '\r' + (' ' * dot_count) + '\r'
+                        print(clearline, end='', flush=True)
                     dot_count = 0
                     return TestResult(name, status, int(time.time() - start_time)), testdir, stdout, stderr
-            print('.', end='', flush=True)
+            if self.use_term_control:
+                print('.', end='', flush=True)
             dot_count += 1
 
     def kill_and_join(self):