Zero return status code when all errors & warnings have been muted - close #933

[Lucas-C]

cf. #933

[Lucas-C]

Tests execution output:

testall.sh: Will process 240 tests from ../cases/testbase/_manifest.txt on 20210331154123
testall.sh: Tidy version in use...
HTML Tidy pour Cygwin version 5.7.45
Testbase is for HTML Tidy version 5.7.21.
========================================
Testing 426885
Testing 427633
Testing 427662
Testing 427664
Testing 427671
Testing 427672
Testing 427675
Testing 427676
Testing 427677
Testing 427810
Testing 427811
Testing 427813
Testing 427816
Testing 427818
Testing 427819
Testing 427820
Testing 427821
Testing 427822
Testing 427823
Testing 427825
Testing 427826
Testing 427827
Testing 427830
Testing 119a
Testing 119b
Testing 119c
Testing 119d
Testing 119e
Testing 119f
Testing 427833
Testing 427834
Testing 427835
Testing 427836
Testing 427837
Testing 427838
Testing 427839
Testing 427840
Testing 427841
Testing 427845
Testing 427846
Testing 431716
Testing 431721
Testing 431731
Testing 431736
Testing 431739
Testing 431874
Testing 431889
Testing 431898
Testing 431964
Testing 432677
Testing 433012
Testing 433021
Testing 433040
Testing 433359
Testing 433360
Testing 433604
Testing 433607
Testing 433656
Testing 433666
Testing 433672
Testing 434047
Testing 434100
Testing 434940
Testing 435903
Testing 435917
Testing 435919
Testing 435920
Testing 435922
Testing 435923
Testing 437468
Testing 438650
Testing 438658
Testing 438954
Testing 438956
Testing 441508
Testing 441568
Testing 443362
Testing 443576
Testing 443678
Testing 445074
Testing 445394
Testing 445557
Testing 449348
Testing 470663
Testing 473490
Testing 480406
Testing 480701
Testing 487204
Testing 487283
Testing 501669
Testing 503436
Testing 504206
Testing 505770
Testing 511679
Testing 511243
Testing 533233
Testing 540571
Testing 543262
Testing 545772
Testing 553468
Testing 566542
Testing 586555
Testing 586562
Testing 588061
Testing 590716
Testing 593705
Testing 609058
Testing 616744
Testing 620531
Testing 629885
Testing 634889
Testing 640473
Testing 640474
Testing 646946
Testing 647255
Testing 647900
Testing 649812
Testing 655338
Testing 656889
Testing 658230
Testing 660397
Testing 671087
Testing 676156
Testing 676205
Testing 678268
Testing 688746
Testing 695408
Testing 696799
Testing 706260
Testing 765852
Testing 795643a
Testing 795643b
Testing 836462a
Testing 836462b
Testing 836462c
Testing 837023
Testing 978947
Testing 996484
Testing 1002509
Testing 1003361
Testing 1004051
Testing 1004512
Testing 1014993
Testing 1015959
Testing 1027888
Testing 1050673
Testing 1052758
Testing 1053626
Testing 1055304
Testing 1055398
Testing 1056023
Testing 1056910
Testing 1062345
Testing 1062511
Testing 1062661
Testing 1063256
Testing 1067112
Testing 1068087
Testing 1069549
Testing 1069553
Testing 1072528
Testing 1078345
Testing 1079820
Testing 1086083
Testing 1090318
Testing 1098012
Testing 1107622
Testing 1117013
Testing 1115094
Testing 1145571
Testing 1145572
Testing 1168193
Testing 1183751
Testing 1198501
Testing 1207443
Testing 1210752
Testing 1231279
Testing 1235296
Testing 1241723
Testing 1263391
Testing 1266647
Testing 1282835
Testing 1286029
Testing 1286278
Testing 1316258
Testing 1316307a
Testing 1316307b
Testing 1326520
Testing 1331849
Testing 1333579
Testing 1359292
Testing 1398397
Testing 1407266
Testing 1408034
Testing 1410061a
Testing 1410061b
Testing 1410061c
Testing 1415137
Testing 1423252
Testing 1426419
Testing 1436578
Testing 1452744
Testing 1445570
Testing 1503897
Testing 1586158
Testing 1590220a
Testing 1590220b
Testing 1603538a
Testing 1603538b
Testing 1610888a
Testing 1610888b
Testing 1632470
Testing 1632218
Testing 1638062
Testing 1674502
Testing 1707836
Testing 1715153
Testing 1720953
Testing 1773932
Testing 1986717a
Testing 1986717b
Testing 1986717c
Testing 2046048
Testing 2085175
Testing 2359929
Testing 2705873a
Testing 2705873b
Testing 2709860
Testing 1642186b
Testing 427664-1
Testing 483
Testing 352
Testing 365
Testing 378a
Testing 378b
Testing 412
Testing 434
Testing 476a
Testing 476b
Testing 629
========================================
testall.sh: Done 240 tests...
run-tests.sh: Running 'diff -ua ../cases/testbase-expects ../cases/testbase-results'
======================================================
======================================================
run-tests.sh: Appear to have PASSED test 2

[balthisar]

Re-opened to invoke the automatic testing.

@Lucas-C, sorry for the backlog. Would you mind merging next into your pr, and then write a test case or two in the new regression_testing directory? You've already done more than most contributors but demonstrating the regression testing, but now the regression testing is even easier, automatic, and it's helpful to include test cases.

[Lucas-C]

I rebased this PR on the next branch of this repo