43206239a8 tests: Add script checking for deterministic line coverage (practicalswift)
Pull request description:
Add script checking for deterministic line coverage in unit tests.
Context: #14343 ("coverage reports non-deterministic")
When the coverage is deterministic this script can be invoked from Travis to guard against regressions, but left inactive for now.
Output in case of determinism:
```
$ contrib/test_deterministic_coverage.sh 2
[2019-01-30 20:08:46] Measuring coverage, run #1 of 2
[2019-01-30 20:10:45] Measuring coverage, run #2 of 2
Coverage test passed: Deterministic coverage across 2 runs.
```
Output in case of non-determinism:
```
$ contrib/test_deterministic_coverage.sh 2
[2019-01-30 20:08:46] Measuring coverage, run #1 of 2
[2019-01-30 20:10:45] Measuring coverage, run #2 of 2
The line coverage is non-deterministic between runs.
The test suite must be deterministic in the sense that the set of lines executed at least
once must be identical between runs. This is a neccessary condition for meaningful coverage
measuring.
--- gcovr.run-1.txt 2019-01-30 23:14:07.419418694 +0100
+++ gcovr.run-2.txt 2019-01-30 23:15:57.998811282 +0100
@@ -471,7 +471,7 @@
test/crypto_tests.cpp 270 270 100%
test/cuckoocache_tests.cpp 142 142 100%
test/dbwrapper_tests.cpp 148 148 100%
-test/denialofservice_tests.cpp 225 225 100%
+test/denialofservice_tests.cpp 225 224 99% 363
test/descriptor_tests.cpp 116 116 100%
test/fs_tests.cpp 24 3 12% 14,16-17,19-20,23,25-26,29,31-32,35-36,39,41-42,45-46,49,51-52
test/getarg_tests.cpp 111 111 100%
@@ -585,5 +585,5 @@
zmq/zmqpublishnotifier.h 5 0 0% 12,31,37,43,49
zmq/zmqrpc.cpp 21 0 0% 16,18,20,22,33-35,38-45,49,52,56,60,62-63
------------------------------------------------------------------------------
-TOTAL 61561 27606 44%
+TOTAL 61561 27605 44%
------------------------------------------------------------------------------
```
In this case line 363 of `test/denialofservice_tests.cpp` was executed only in the second run. Non-determinism detected!
Tree-SHA512: 03f45590e70a87146f89aa7838beeff0925d7fd303697ff03e0e69f8a5861694be5f0dd10cb0020e3e3d40c9cf662f71dfcd838f6affb31bd5212314e0a4e3a9
