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demonstrate how to quickly find a problematic commit that introduced a bug in quite big commits tree

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git bisect command Demo

Goal - to demonstrate how to quickly find a problematic commit that introduced a bug in quite big commits tree.

In order to show it, I'll use a simple spring boot application..

Procedure

  1. Start the bisect on main branch
 [zgrinber@zgrinber git-bisect-demo]$ git bisect start
  1. Define a bad commit(current commit pointed by main branch and HEAD)
 [zgrinber@zgrinber git-bisect-demo]$  git bisect bad
  1. Define a good commit(pointed by first version denoted by tag V1.0) that the application worked and tests were passed successfully
 [zgrinber@zgrinber git-bisect-demo]$  git bisect good V1.0
 Bisecting: 396 revisions left to test after this (roughly 9 steps)
[c11e9e4086a6bb4e83241463c498320001df2ce6] add new phonetic mapping 403
  1. test the current checkouted commit:
 [zgrinber@zgrinber git-bisect-demo]$ mvn clean test
 2022-07-31 12:27:41.158  INFO 88241 --- [           main] t.c.s.AnnotationConfigContextLoaderUtils : Could not detect default configuration classes for test class [controller.MyControllerTest]: MyControllerTest does not declare any static, non-private, non-final, nested classes annotated with @Configuration.
[ERROR] Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.017 s <<< FAILURE! - in controller.MyControllerTest
[ERROR] controller.MyControllerTest  Time elapsed: 0.016 s  <<< ERROR!
java.lang.IllegalStateException: Unable to find a @SpringBootConfiguration, you need to use @ContextConfiguration or @SpringBootTest(classes=...) with your test

[INFO] 
[INFO] Results:
[INFO] 
[ERROR] Errors: 
[ERROR]   MyControllerTest » IllegalState Unable to find a @SpringBootConfiguration, you...
[INFO] 
[ERROR] Tests run: 2, Failures: 0, Errors: 1, Skipped: 0
[INFO] 
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  4.323 s
[INFO] Finished at: 2022-07-31T12:27:41+03:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-surefire-plugin:2.22.2:test (default-test) on project test-demo: There are test failures.
[ERROR] 
[ERROR] Please refer to /home/zgrinber/git/git-bisect-demo/target/surefire-reports for the individual test results.
[ERROR] Please refer to dump files (if any exist) [date].dump, [date]-jvmRun[N].dump and [date].dumpstream.
[ERROR] -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
  1. We failed on the test, then we'll tell git bisect that this is also a bad commit
[zgrinber@zgrinber git-bisect-demo]$ git bisect bad
Bisecting: 198 revisions left to test after this (roughly 8 steps)
[fe446c4b3295c095886aa71d3c9fa1141e2b5975] add new phonetic mapping 205
  1. Let's test the current commit that git bisect checked out:
[zgrinber@zgrinber git-bisect-demo]$ mvn clean test

[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.411 s - in com.redhat.zvikag.testdemo.controller.MyControllerTest
[INFO] 
[INFO] Results:
[INFO] 
[INFO] Tests run: 2, Failures: 0, Errors: 0, Skipped: 0
[INFO] 
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  4.692 s
[INFO] Finished at: 2022-07-31T12:32:30+03:00
[INFO] ------------------------------------------------------------------------

7.Tested of the current commit succeeded, then we'll tell git bisect that this commit is good

[zgrinber@zgrinber git-bisect-demo]$ git bisect good
Bisecting: 99 revisions left to test after this (roughly 7 steps)
[72626011b1a64ae0e3e52ea25b0ec4915dad2994] add new phonetic mapping 304

8.We already narrowed down the range of commits to tests to 99 instead of 793 commits.
We will continue in the same way, by testing each checked out commit, and tell git bisect if it's a good or bad commit. in this case, we'll get a series of good commits, until we'll find the problematic commit that broke the code

  [zgrinber@zgrinber git-bisect-demo]$ mvn clean test 
  [INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.421 s - in com.redhat.zvikag.testdemo.controller.MyControllerTest
  [INFO] 
  [INFO] Results:
  [INFO] 
  [INFO] Tests run: 2, Failures: 0, Errors: 0, Skipped: 0
  [INFO] 
  [INFO] ------------------------------------------------------------------------
  [INFO] BUILD SUCCESS
  [INFO] ------------------------------------------------------------------------
  [INFO] Total time:  4.668 s
  [INFO] Finished at: 2022-07-31T12:37:19+03:00
  [INFO] ------------------------------------------------------------------------
  [zgrinber@zgrinber git-bisect-demo]$ git bisect good
  Bisecting: 49 revisions left to test after this (roughly 6 steps)
  [05c1929fc1eabd2151262032ddc15d33288efdd0] add new phonetic mapping 354
  [zgrinber@zgrinber git-bisect-demo]$ mvn clean test 
  [INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.421 s - in com.redhat.zvikag.testdemo.controller.MyControllerTest
  [INFO] 
  [INFO] Results:
  [INFO] 
  [INFO] Tests run: 2, Failures: 0, Errors: 0, Skipped: 0
  [INFO] 
  [INFO] ------------------------------------------------------------------------
  [INFO] BUILD SUCCESS
  [INFO] ------------------------------------------------------------------------
  [INFO] Total time:  4.668 s
  [INFO] Finished at: 2022-07-31T12:37:19+03:00
  [INFO] ------------------------------------------------------------------------
  [zgrinber@zgrinber git-bisect-demo]$ 
  [zgrinber@zgrinber git-bisect-demo]$ git bisect good
  Bisecting: 24 revisions left to test after this (roughly 5 steps)
  [7fab4ede68b80d338bcec58674aa4a3252f28dbd] add new phonetic mapping 379
  [zgrinber@zgrinber git-bisect-demo]$
  [zgrinber@zgrinber git-bisect-demo]$ mvn clean test 
  [INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.421 s - in com.redhat.zvikag.testdemo.controller.MyControllerTest
  [INFO] 
  [INFO] Results:
  [INFO] 
  [INFO] Tests run: 2, Failures: 0, Errors: 0, Skipped: 0
  [INFO] 
  [INFO] ------------------------------------------------------------------------
  [INFO] BUILD SUCCESS
  [INFO] ------------------------------------------------------------------------
  [INFO] Total time:  4.668 s
  [INFO] Finished at: 2022-07-31T12:37:19+03:00
  [INFO] ------------------------------------------------------------------------
  [zgrinber@zgrinber git-bisect-demo]$ 
  [zgrinber@zgrinber git-bisect-demo]$ git bisect good
  Bisecting: 12 revisions left to test after this (roughly 4 steps)
  [7e52dec81ff48d8eadbeb99c1fb7714f163d0c74] add new phonetic mapping 391
  [zgrinber@zgrinber git-bisect-demo]$ mvn clean test 
  [INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.421 s - in com.redhat.zvikag.testdemo.controller.MyControllerTest
  [INFO] 
  [INFO] Results:
  [INFO] 
  [INFO] Tests run: 2, Failures: 0, Errors: 0, Skipped: 0
  [INFO] 
  [INFO] ------------------------------------------------------------------------
  [INFO] BUILD SUCCESS
  [INFO] ------------------------------------------------------------------------
  [INFO] Total time:  4.668 s
  [INFO] Finished at: 2022-07-31T12:37:19+03:00
  [INFO] ------------------------------------------------------------------------
  [zgrinber@zgrinber git-bisect-demo]$ 
  [zgrinber@zgrinber git-bisect-demo]$ git bisect good
  Bisecting: 6 revisions left to test after this (roughly 3 steps)
  [4d44ad8a5825d7da3564bf8bed9e112bf96ba1e8] add new phonetic mapping 397
  [zgrinber@zgrinber git-bisect-demo]$ 
  [zgrinber@zgrinber git-bisect-demo]$ mvn clean test 
  [INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.421 s - in com.redhat.zvikag.testdemo.controller.MyControllerTest
  [INFO] 
  [INFO] Results:
  [INFO] 
  [INFO] Tests run: 2, Failures: 0, Errors: 0, Skipped: 0
  [INFO] 
  [INFO] ------------------------------------------------------------------------
  [INFO] BUILD SUCCESS
  [INFO] ------------------------------------------------------------------------
  [INFO] Total time:  4.668 s
  [INFO] Finished at: 2022-07-31T12:37:19+03:00
  [INFO] ------------------------------------------------------------------------
  [zgrinber@zgrinber git-bisect-demo]$ 
  [zgrinber@zgrinber git-bisect-demo]$ git bisect good
  Bisecting: 3 revisions left to test after this (roughly 2 steps)
  [43b3ff204bebcbe8f5be1a5ec7546574d780da74] add new phonetic mapping 400
  [zgrinber@zgrinber git-bisect-demo]$ 
  [zgrinber@zgrinber git-bisect-demo]$ mvn clean test 
  [INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.421 s - in com.redhat.zvikag.testdemo.controller.MyControllerTest
  [INFO] 
  [INFO] Results:
  [INFO] 
  [INFO] Tests run: 2, Failures: 0, Errors: 0, Skipped: 0
  [INFO] 
  [INFO] ------------------------------------------------------------------------
  [INFO] BUILD SUCCESS
  [INFO] ------------------------------------------------------------------------
  [INFO] Total time:  4.668 s
  [INFO] Finished at: 2022-07-31T12:37:19+03:00
  [INFO] ------------------------------------------------------------------------
  [zgrinber@zgrinber git-bisect-demo]$ 
  [zgrinber@zgrinber git-bisect-demo]$ git bisect good
  Bisecting: 1 revision left to test after this (roughly 1 step)
  [869e2cc5194ad13141c1742011e883ca3996cdc2] add new phonetic mapping 401
  [zgrinber@zgrinber git-bisect-demo]$ 
  [zgrinber@zgrinber git-bisect-demo]$ mvn clean test
  [ERROR] Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.015 s <<< FAILURE! - in controller.MyControllerTest
  [ERROR] controller.MyControllerTest  Time elapsed: 0.015 s  <<< ERROR!
  java.lang.IllegalStateException: Unable to find a @SpringBootConfiguration, you need to use @ContextConfiguration or @SpringBootTest(classes=...) 
   with your test

  [INFO] 
  [INFO] Results:
  [INFO] 
  [ERROR] Errors: 
  [ERROR]   MyControllerTest » IllegalState Unable to find a @SpringBootConfiguration, you...
  [INFO] 
  [ERROR] Tests run: 2, Failures: 0, Errors: 1, Skipped: 0
  [INFO] 
  [INFO] ------------------------------------------------------------------------
  [INFO] BUILD FAILURE
  [INFO] ------------------------------------------------------------------------
  [INFO] Total time:  4.224 s
  [INFO] Finished at: 2022-07-31T13:49:45+03:00
  [INFO] ------------------------------------------------------------------------
  [ERROR] Failed to execute goal org.apache.maven.plugins:maven-surefire-plugin:2.22.2:test (default-test) on project test-demo: There are test  
  failures.

9. The last checkout commit failed, so we're marking it as bad
```shell
[zgrinber@zgrinber git-bisect-demo]$ git bisect bad 
Bisecting: 0 revisions left to test after this (roughly 0 steps)
[6d2e3d8f42180aeadc9bfc87670862492bd8cb91] problematic commit that breaks the code

And we got the problematic commit

  1. now current checked out commit is the problematic one, so tag it with a name
[zgrinber@zgrinber git-bisect-demo]$ git tag problematicVersion
  1. show the full log of the bisect:
[zgrinber@zgrinber git-bisect-demo]$ git bisect log
git bisect start
# bad: [dee7d4814ac87b2e8a7285b0ba4d30e0d3ca95ae] add new phonetic mapping 800
git bisect bad dee7d4814ac87b2e8a7285b0ba4d30e0d3ca95ae
# good: [1fb23c8a088f2429f152e472dfa7ca9e0961e429] first working revision
git bisect good 1fb23c8a088f2429f152e472dfa7ca9e0961e429
# bad: [c11e9e4086a6bb4e83241463c498320001df2ce6] add new phonetic mapping 403
git bisect bad c11e9e4086a6bb4e83241463c498320001df2ce6
# good: [fe446c4b3295c095886aa71d3c9fa1141e2b5975] add new phonetic mapping 205
git bisect good fe446c4b3295c095886aa71d3c9fa1141e2b5975
# good: [72626011b1a64ae0e3e52ea25b0ec4915dad2994] add new phonetic mapping 304
git bisect good 72626011b1a64ae0e3e52ea25b0ec4915dad2994
# good: [05c1929fc1eabd2151262032ddc15d33288efdd0] add new phonetic mapping 354
git bisect good 05c1929fc1eabd2151262032ddc15d33288efdd0
# good: [7fab4ede68b80d338bcec58674aa4a3252f28dbd] add new phonetic mapping 379
git bisect good 7fab4ede68b80d338bcec58674aa4a3252f28dbd
# good: [7e52dec81ff48d8eadbeb99c1fb7714f163d0c74] add new phonetic mapping 391
git bisect good 7e52dec81ff48d8eadbeb99c1fb7714f163d0c74
# good: [4d44ad8a5825d7da3564bf8bed9e112bf96ba1e8] add new phonetic mapping 397
git bisect good 4d44ad8a5825d7da3564bf8bed9e112bf96ba1e8
# good: [43b3ff204bebcbe8f5be1a5ec7546574d780da74] add new phonetic mapping 400
git bisect good 43b3ff204bebcbe8f5be1a5ec7546574d780da74
# bad: [869e2cc5194ad13141c1742011e883ca3996cdc2] add new phonetic mapping 401
git bisect bad 869e2cc5194ad13141c1742011e883ca3996cdc2
[zgrinber@zgrinber git-bisect-demo]$

Note: After checking only 10 commits,out of almost 800 commits, we identified the problematic commit!.

  1. end the bisect process by the following command
[zgrinber@zgrinber git-bisect-demo]$ git bisect reset 
Previous HEAD position was 6d2e3d8 problematic commit that breaks the code
Switched to branch 'main'
  1. Now create new branch fixBug:
[zgrinber@zgrinber git-bisect-demo]$ git checkout -b fixBug
Switched to a new branch 'fixBug'
  1. We're about toe revert the problematic commit, Just verify that the code is broken before reverting the commit
[zgrinber@zgrinber git-bisect-demo]$ mvn clean test
[ERROR] Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.01 s <<< FAILURE! - in controller.MyControllerTest
[ERROR] controller.MyControllerTest  Time elapsed: 0.01 s  <<< ERROR!
java.lang.IllegalStateException: Unable to find a @SpringBootConfiguration, you need to use @ContextConfiguration or @SpringBootTest(classes=...) with your test

[INFO] 
[INFO] Results:
[INFO] 
[ERROR] Errors: 
[ERROR]   MyControllerTest » IllegalState Unable to find a @SpringBootConfiguration, you...
[INFO] 
[ERROR] Tests run: 2, Failures: 0, Errors: 1, Skipped: 0
[INFO] 
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  4.333 s
[INFO] Finished at: 2022-07-31T14:03:01+03:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-surefire-plugin:2.22.2:test (default-test) on project test-demo: There are test failures.
  1. Revert the problematic commit using git revert command and problematicVersion tag that points to the problematic commit:
[zgrinber@zgrinber git-bisect-demo]$ git revert problematicVersion

You'll see an editor screen, just save it or quit it, and a new commit that reverting the problematic one will be created.

  1. Verify that the issue was fixed
[zgrinber@zgrinber git-bisect-demo]$ mvn clean test
2022-07-31 14:06:57.708  INFO 104535 --- [           main] o.s.t.web.servlet.TestDispatcherServlet  : Completed initialization in 0 ms
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.553 s - in com.redhat.zvikag.testdemo.controller.MyControllerTest
[INFO] 
[INFO] Results:
[INFO] 
[INFO] Tests run: 2, Failures: 0, Errors: 0, Skipped: 0
[INFO] 
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  4.809 s
[INFO] Finished at: 2022-07-31T14:06:58+03:00
[INFO] ------------------------------------------------------------------------
[zgrinber@zgrinber git-bisect-demo]$
  1. Now push to remote upstream and open PR from fixBug to main on github, or on local git repo, merge fixBug into main and push to remote
[zgrinber@zgrinber git-bisect-demo]$ git checkout main ; git merge fixBug --ff-only ; git push

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demonstrate how to quickly find a problematic commit that introduced a bug in quite big commits tree

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