ক্যাপস্টোন — requirement থেকে release পর্যন্ত একটি পূর্ণ project, Git workflow-সহ

$ git -c init.defaultBranch=main init
Initialized empty Git repository in …/rahim/.git/
$ git config user.name "Rahim"
$ git config user.email "rahim@example.com"
$ git config core.autocrlf false
$ git config pull.ff only
$ git config fetch.prune true
$ git add .
$ git status --short
A  .gitignore
A  CONTRIBUTING.md
A  README.md
A  docs/adr/0001-in-memory-store.md
A  lending.py
$ git commit -m "chore: initial project skeleton"
[main (root-commit) a323299] chore: initial project skeleton
 5 files changed, 30 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 CONTRIBUTING.md
 create mode 100644 README.md
 create mode 100644 docs/adr/0001-in-memory-store.md
 create mode 100644 lending.py
$ git add .github
$ git commit -m "ci: add lint and test workflow"
[main 4a99fdc] ci: add lint and test workflow
 1 file changed, 23 insertions(+)
 create mode 100644 .github/workflows/ci.yml
$ git remote add origin ../origin.git
$ git push -u origin main
To ../origin.git
 * [new branch]      main -> main
branch 'main' set up to track 'origin/main'.

$ git clone -c core.autocrlf=false origin.git nasrin
Cloning into 'nasrin'...
done.
$ git remote set-url origin ../origin.git
$ git config user.name "Nasrin"
$ git config user.email "nasrin@example.com"
$ git config pull.ff only
$ git config fetch.prune true
$ git log --oneline
4a99fdc ci: add lint and test workflow
a323299 chore: initial project skeleton

$ git switch -c feature/borrow
Switched to a new branch 'feature/borrow'
$ python -m unittest
E
======================================================================
ERROR: test_borrow (unittest.loader._FailedTest.test_borrow)
----------------------------------------------------------------------
ImportError: Failed to import test module: test_borrow
Traceback (most recent call last):
…
ImportError: cannot import name 'Library' from 'lending' (…\rahim\lending.py)


----------------------------------------------------------------------
Ran 1 test in 0.000s

FAILED (errors=1)
$ python -m unittest -v
test_borrowed_book_is_on_loan (test_borrow.BorrowTest.test_borrowed_book_is_on_loan) ... ok
test_returned_book_is_no_longer_on_loan (test_borrow.BorrowTest.test_returned_book_is_no_longer_on_loan) ... ok

----------------------------------------------------------------------
Ran 2 tests in 0.000s

OK
$ git add lending.py test_borrow.py
$ git commit -m "feat(borrow): borrow and return books" -m "Covers stories S1 and S2: a member borrows a book and returns it."
[feature/borrow 86970bb] feat(borrow): borrow and return books
 2 files changed, 32 insertions(+)
 create mode 100644 test_borrow.py
$ git push -u origin feature/borrow
To ../origin.git
 * [new branch]      feature/borrow -> feature/borrow
branch 'feature/borrow' set up to track 'origin/feature/borrow'.

import sys, unittest
from datetime import date, timedelta
# --- lending.py as tagged v1.0.1 (blank lines squeezed to fit the page)
LOAN_DAYS = 14
FINE_PER_DAY = 5  # taka
def days_late(borrowed_on, today):
    return (today - borrowed_on).days - LOAN_DAYS
def fine(borrowed_on, returned_on):
    return max(0, days_late(borrowed_on, returned_on)) * FINE_PER_DAY
class Library:
    def __init__(self):
        self.loans = {}  # book -> (member, borrowed_on)
    def borrow(self, book, member, day):
        if book in self.loans:
            raise ValueError(f"{book} is already borrowed")
        self.loans[book] = (member, day)
    def give_back(self, book, day):
        _, borrowed_on = self.loans.pop(book)
        return fine(borrowed_on, day)
    def overdue(self, today):
        return sorted(book for book, (_, day) in self.loans.items()
                      if days_late(day, today) > 0)
# --- the acceptance criteria as tests (condensed from test_*.py)
D = date(2026, 2, 2)
class Lending(unittest.TestCase):
    def setUp(self): self.lib = Library(); self.lib.borrow("B1", "M1", D)
    def test_s3_book_on_loan_cannot_be_borrowed(self):
        with self.assertRaises(ValueError): self.lib.borrow("B1", "M2", D)
    def test_s2_returned_book_leaves_loans(self):
        self.lib.give_back("B1", D); self.assertNotIn("B1", self.lib.loans)
    def test_s4_three_days_late_costs_15(self): self.assertEqual(self.lib.give_back("B1", D + timedelta(17)), 15)
    def test_s4_early_return_is_free(self): self.assertEqual(self.lib.give_back("B1", D + timedelta(10)), 0)
    def test_s5_due_date_is_not_overdue(self): self.assertEqual(self.lib.overdue(D + timedelta(14)), [])
    def test_s5_next_day_is_overdue(self): self.assertEqual(self.lib.overdue(D + timedelta(15)), ["B1"])
unittest.TextTestRunner(stream=sys.stdout, verbosity=2).run(unittest.defaultTestLoader.loadTestsFromTestCase(Lending))

$ python -m unittest
...
----------------------------------------------------------------------
Ran 3 tests in 0.000s

OK
$ git add test_borrow.py
$ git commit -m "test(borrow): reject borrowing a book that is on loan" -m "Story S3 had code but no test (review comment on PR #1)."
[feature/borrow e311026] test(borrow): reject borrowing a book that is on loan
 1 file changed, 6 insertions(+)
$ git push
To ../origin.git
   86970bb..e311026  feature/borrow -> feature/borrow
$ git switch main
Switched to branch 'main'
Your branch is up to date with 'origin/main'.
$ git pull
From ../origin
 * [new branch]      feature/fine -> origin/feature/fine
Already up to date.
$ git merge --no-ff feature/borrow -m "Merge pull request #1 from feature/borrow"
Merge made by the 'ort' strategy.
 lending.py     | 13 +++++++++++++
 test_borrow.py | 25 +++++++++++++++++++++++++
 2 files changed, 38 insertions(+)
 create mode 100644 test_borrow.py
$ git push
To ../origin.git
   4a99fdc..63acace  main -> main
$ git branch -d feature/borrow
Deleted branch feature/borrow (was e311026).
$ git push origin --delete feature/borrow
To ../origin.git
 - [deleted]         feature/borrow

$ git switch main
Switched to branch 'main'
Your branch is up to date with 'origin/main'.
$ git pull
From ../origin
   4a99fdc..63acace  main       -> origin/main
Updating 4a99fdc..63acace
Fast-forward
 lending.py     | 13 +++++++++++++
 test_borrow.py | 25 +++++++++++++++++++++++++
 2 files changed, 38 insertions(+)
 create mode 100644 test_borrow.py
$ git switch feature/fine
Switched to branch 'feature/fine'
Your branch is up to date with 'origin/feature/fine'.
$ git rebase main
Rebasing (1/1)
Auto-merging lending.py
CONFLICT (content): Merge conflict in lending.py
error: could not apply 92d14d8... feat(fine): charge 5 taka per late day
hint: Resolve all conflicts manually, mark them as resolved with
hint: "git add/rm <conflicted_files>", then run "git rebase --continue".
hint: You can instead skip this commit: run "git rebase --skip".
hint: To abort and get back to the state before "git rebase", run "git rebase --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Could not apply 92d14d8... # feat(fine): charge 5 taka per late day
$ git status
interactive rebase in progress; onto 63acace
Last command done (1 command done):
   pick 92d14d8 # feat(fine): charge 5 taka per late day
No commands remaining.
You are currently rebasing branch 'feature/fine' on '63acace'.
  (fix conflicts and then run "git rebase --continue")
  (use "git rebase --skip" to skip this patch)
  (use "git rebase --abort" to check out the original branch)

Changes to be committed:
  (use "git restore --staged <file>..." to unstage)
	new file:   test_fine.py

Unmerged paths:
  (use "git restore --staged <file>..." to unstage)
  (use "git add <file>..." to mark resolution)
	both modified:   lending.py

$ cat lending.py
"""Library lending core (fictional demo project)."""

LOAN_DAYS = 14
<<<<<<< HEAD


class Library:
    def __init__(self):
        self.loans = {}  # book -> (member, borrowed_on)

    def borrow(self, book, member, day):
        if book in self.loans:
            raise ValueError(f"{book} is already borrowed")
        self.loans[book] = (member, day)

    def give_back(self, book, day):
        self.loans.pop(book)
=======
FINE_PER_DAY = 5  # taka


def fine(borrowed_on, returned_on):
    late = (returned_on - borrowed_on).days - LOAN_DAYS
    return max(0, late) * FINE_PER_DAY
>>>>>>> 92d14d8 (feat(fine): charge 5 taka per late day)
$ python -m unittest
.....
----------------------------------------------------------------------
Ran 5 tests in 0.000s

OK
$ git add lending.py
$ git rebase --continue
[detached HEAD cadacb4] feat(fine): charge 5 taka per late day
 2 files changed, 20 insertions(+)
 create mode 100644 test_fine.py
Successfully rebased and updated refs/heads/feature/fine.
$ git log --oneline --graph -5
* cadacb4 feat(fine): charge 5 taka per late day
*   63acace Merge pull request #1 from feature/borrow
|\  
| * e311026 test(borrow): reject borrowing a book that is on loan
| * 86970bb feat(borrow): borrow and return books
|/  
* 4a99fdc ci: add lint and test workflow
$ python -m unittest
......
----------------------------------------------------------------------
Ran 6 tests in 0.000s

OK
$ git add lending.py test_fine.py
$ git commit -m "feat(fine): return the fine from give_back" -m "Acceptance criterion of S4 (review comment on PR #2)."
[feature/fine 4db12a0] feat(fine): return the fine from give_back
 2 files changed, 8 insertions(+), 2 deletions(-)
$ git push
To ../origin.git
 ! [rejected]        feature/fine -> feature/fine (non-fast-forward)
error: failed to push some refs to '../origin.git'
hint: Updates were rejected because the tip of your current branch is behind
hint: its remote counterpart. If you want to integrate the remote changes,
hint: use 'git pull' before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.
$ git push --force-with-lease
To ../origin.git
 + 92d14d8...4db12a0 feature/fine -> feature/fine (forced update)

$ git switch main
Switched to branch 'main'
Your branch is up to date with 'origin/main'.
$ git pull
Already up to date.
$ git merge --no-ff feature/fine -m "Merge pull request #2 from feature/fine"
Merge made by the 'ort' strategy.
 lending.py   |  9 ++++++++-
 test_fine.py | 19 +++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 test_fine.py
$ git push
To ../origin.git
   63acace..609f70f  main -> main
$ git branch -d feature/fine
Deleted branch feature/fine (was 4db12a0).
$ git push origin --delete feature/fine
To ../origin.git
 - [deleted]         feature/fine

$ git switch -c release/1.0.0
Switched to a new branch 'release/1.0.0'
$ git add CHANGELOG.md
$ git commit -m "chore(release): 1.0.0"
[release/1.0.0 1aee4eb] chore(release): 1.0.0
 1 file changed, 11 insertions(+)
 create mode 100644 CHANGELOG.md
$ git push -u origin release/1.0.0
To ../origin.git
 * [new branch]      release/1.0.0 -> release/1.0.0
branch 'release/1.0.0' set up to track 'origin/release/1.0.0'.
$ git switch main
Switched to branch 'main'
Your branch is up to date with 'origin/main'.
$ git pull
Already up to date.
$ git merge --no-ff release/1.0.0 -m "Merge pull request #6 from release/1.0.0"
Merge made by the 'ort' strategy.
 CHANGELOG.md | 11 +++++++++++
 1 file changed, 11 insertions(+)
 create mode 100644 CHANGELOG.md
$ git tag -a v1.0.0 -m "lending 1.0.0"
$ git push --follow-tags
To ../origin.git
   516d42b..60c8dab  main -> main
 * [new tag]         v1.0.0 -> v1.0.0
$ git describe
v1.0.0
$ git branch -d release/1.0.0
Deleted branch release/1.0.0 (was 1aee4eb).
$ git push origin --delete release/1.0.0
To ../origin.git
 - [deleted]         release/1.0.0
$ git log --graph --oneline -12
*   60c8dab Merge pull request #6 from release/1.0.0
|\  
| * 1aee4eb chore(release): 1.0.0
|/  
*   516d42b Merge pull request #5 from docs/usage
|\  
| * 27ca69e docs(readme): add a usage example
|/  
*   af97afe Merge pull request #4 from refactor/days-late
|\  
| * 1f8d3cb test(report): cover the due-date boundary
| * 72cb901 refactor(lending): extract days_late helper
|/  
*   1bebbf6 Merge pull request #3 from feature/overdue
|\  
| * 63bd2c0 feat(report): list overdue loans
|/  
*   609f70f Merge pull request #2 from feature/fine
|\  
| * 4db12a0 feat(fine): return the fine from give_back
| * cadacb4 feat(fine): charge 5 taka per late day

$ git log --graph --oneline --all
*   60b78d1 Merge pull request #8 from fix/negative-fine
|\  
| * 5b3fc4f chore(release): 1.0.1
| * da9e35e fix(fine): never charge a negative fine
|/  
*   60c8dab Merge pull request #6 from release/1.0.0
|\  
| * 1aee4eb chore(release): 1.0.0
|/  
*   516d42b Merge pull request #5 from docs/usage
|\  
| * 27ca69e docs(readme): add a usage example
|/  
*   af97afe Merge pull request #4 from refactor/days-late
|\  
| * 1f8d3cb test(report): cover the due-date boundary
| * 72cb901 refactor(lending): extract days_late helper
|/  
*   1bebbf6 Merge pull request #3 from feature/overdue
|\  
| * 63bd2c0 feat(report): list overdue loans
|/  
*   609f70f Merge pull request #2 from feature/fine
|\  
| * 4db12a0 feat(fine): return the fine from give_back
| * cadacb4 feat(fine): charge 5 taka per late day
|/  
*   63acace Merge pull request #1 from feature/borrow
|\  
| * e311026 test(borrow): reject borrowing a book that is on loan
| * 86970bb feat(borrow): borrow and return books
|/  
* 4a99fdc ci: add lint and test workflow
* a323299 chore: initial project skeleton
$ git tag -n
v1.0.0          lending 1.0.0
v1.0.1          lending 1.0.1

$ python -m unittest discover -s ../regress
F
======================================================================
FAIL: test_early_return_is_free (test_issue7.Issue7.test_early_return_is_free)
----------------------------------------------------------------------
Traceback (most recent call last):
…
AssertionError: -20 != 0

----------------------------------------------------------------------
Ran 1 test in 0.000s

FAILED (failures=1)
$ git switch --detach 609f70f
HEAD is now at 609f70f Merge pull request #2 from feature/fine
$ python -m unittest discover -s ../regress
.
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK
$ git switch main
Previous HEAD position was 609f70f Merge pull request #2 from feature/fine
Switched to branch 'main'
Your branch is up to date with 'origin/main'.

$ git bisect start v1.0.0 609f70f
Bisecting: 3 revisions left to test after this (roughly 2 steps)
[af97afe2bdbfa5c8252095772dbf8788f505a79b] Merge pull request #4 from refactor/days-late
$ git bisect run python -m unittest discover -s ../regress
running 'python' '-m' 'unittest' 'discover' '-s' '../regress'
F
======================================================================
FAIL: test_early_return_is_free (test_issue7.Issue7.test_early_return_is_free)
----------------------------------------------------------------------
Traceback (most recent call last):
…
AssertionError: -20 != 0

----------------------------------------------------------------------
Ran 1 test in 0.000s

FAILED (failures=1)
Bisecting: 2 revisions left to test after this (roughly 1 step)
[1bebbf6a53686e2ab52dae4262c378af5ba4fb7a] Merge pull request #3 from feature/overdue
running 'python' '-m' 'unittest' 'discover' '-s' '../regress'
.
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK
Bisecting: 0 revisions left to test after this (roughly 1 step)
[1f8d3cb6b507a1556694de11b0db30392384bd21] test(report): cover the due-date boundary
running 'python' '-m' 'unittest' 'discover' '-s' '../regress'
F
======================================================================
FAIL: test_early_return_is_free (test_issue7.Issue7.test_early_return_is_free)
----------------------------------------------------------------------
Traceback (most recent call last):
…
AssertionError: -20 != 0

----------------------------------------------------------------------
Ran 1 test in 0.000s

FAILED (failures=1)
Bisecting: 0 revisions left to test after this (roughly 0 steps)
[72cb9012a7b9866d170d303871dc1682b2b4ccaa] refactor(lending): extract days_late helper
running 'python' '-m' 'unittest' 'discover' '-s' '../regress'
F
======================================================================
FAIL: test_early_return_is_free (test_issue7.Issue7.test_early_return_is_free)
----------------------------------------------------------------------
Traceback (most recent call last):
…
AssertionError: -20 != 0

----------------------------------------------------------------------
Ran 1 test in 0.000s

FAILED (failures=1)
72cb9012a7b9866d170d303871dc1682b2b4ccaa is the first bad commit
commit 72cb9012a7b9866d170d303871dc1682b2b4ccaa
Author: Rahim <rahim@example.com>
Date:   Tue Feb 10 10:30:00 2026 +0600

    refactor(lending): extract days_late helper
    
    fine() and overdue() repeated the 14-day rule (review note on PR #3).

 lending.py | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)
bisect found first bad commit
$ git bisect log
# bad: [60c8dabf100ce0eace81e68950a3eeff501799bc] Merge pull request #6 from release/1.0.0
# good: [609f70fb0536d5453a5252e24ca5a1a5696719b3] Merge pull request #2 from feature/fine
git bisect start 'v1.0.0' '609f70f'
# bad: [af97afe2bdbfa5c8252095772dbf8788f505a79b] Merge pull request #4 from refactor/days-late
git bisect bad af97afe2bdbfa5c8252095772dbf8788f505a79b
# good: [1bebbf6a53686e2ab52dae4262c378af5ba4fb7a] Merge pull request #3 from feature/overdue
git bisect good 1bebbf6a53686e2ab52dae4262c378af5ba4fb7a
# bad: [1f8d3cb6b507a1556694de11b0db30392384bd21] test(report): cover the due-date boundary
git bisect bad 1f8d3cb6b507a1556694de11b0db30392384bd21
# bad: [72cb9012a7b9866d170d303871dc1682b2b4ccaa] refactor(lending): extract days_late helper
git bisect bad 72cb9012a7b9866d170d303871dc1682b2b4ccaa
# first bad commit: [72cb9012a7b9866d170d303871dc1682b2b4ccaa] refactor(lending): extract days_late helper
$ git bisect reset
Previous HEAD position was 72cb901 refactor(lending): extract days_late helper
Switched to branch 'main'
Your branch is up to date with 'origin/main'.

$ git show 72cb901 -- lending.py
commit 72cb9012a7b9866d170d303871dc1682b2b4ccaa
Author: Rahim <rahim@example.com>
Date:   Tue Feb 10 10:30:00 2026 +0600

    refactor(lending): extract days_late helper
    
    fine() and overdue() repeated the 14-day rule (review note on PR #3).

diff --git a/lending.py b/lending.py
index eec4800..3ed686e 100644
--- a/lending.py
+++ b/lending.py
@@ -4,9 +4,12 @@ LOAN_DAYS = 14
 FINE_PER_DAY = 5  # taka
 
 
+def days_late(borrowed_on, today):
+    return (today - borrowed_on).days - LOAN_DAYS
+
+
 def fine(borrowed_on, returned_on):
-    late = (returned_on - borrowed_on).days - LOAN_DAYS
-    return max(0, late) * FINE_PER_DAY
+    return days_late(borrowed_on, returned_on) * FINE_PER_DAY
 
 
 class Library:
@@ -24,4 +27,4 @@ class Library:
 
     def overdue(self, today):
         return sorted(book for book, (_, day) in self.loans.items()
-                      if (today - day).days > LOAN_DAYS)
+                      if days_late(day, today) > 0)

import io, unittest
from datetime import date, timedelta
LOAN_DAYS, FINE_PER_DAY = 14, 5
def days_late(borrowed_on, today):
    return (today - borrowed_on).days - LOAN_DAYS

def fine_buggy(borrowed_on, returned_on):   # after 72cb901 (in v1.0.0)
    return days_late(borrowed_on, returned_on) * FINE_PER_DAY

def fine_fixed(borrowed_on, returned_on):   # after da9e35e (in v1.0.1)
    return max(0, days_late(borrowed_on, returned_on)) * FINE_PER_DAY

def regression_suite(fine):
    class Issue7(unittest.TestCase):         # the test from the bug report
        def test_early_return_is_free(self):
            d = date(2026, 2, 2)
            self.assertEqual(fine(d, d + timedelta(days=10)), 0)
        def test_old_behaviour_kept(self):      # 14 days free, 17 days 15 taka
            d = date(2026, 2, 2)
            self.assertEqual([fine(d, d + timedelta(days=n)) for n in (14, 17)], [0, 15])
    return unittest.defaultTestLoader.loadTestsFromTestCase(Issue7)

for f in (fine_buggy, fine_fixed):
    log = io.StringIO()
    r = unittest.TextTestRunner(stream=log).run(regression_suite(f))
    print(f"{f.__name__}: ran {r.testsRun}, failures {len(r.failures)}"
          f" -> {'PASS' if r.wasSuccessful() else 'FAIL'}")
    for test, tb in r.failures:
        print("   ", test.id().split(".")[-1], "|", tb.strip().splitlines()[-1])
print("fine for 3, 10, 14, 15, 20 days:",
      [fine_buggy(date(2026, 2, 2), date(2026, 2, 2) + timedelta(n)) for n in (3, 10, 14, 15, 20)],
      [fine_fixed(date(2026, 2, 2), date(2026, 2, 2) + timedelta(n)) for n in (3, 10, 14, 15, 20)])

$ git switch -c fix/negative-fine
Switched to a new branch 'fix/negative-fine'
$ python -m unittest
...F.....
======================================================================
FAIL: test_early_return_is_free (test_fine.FineTest.test_early_return_is_free)
----------------------------------------------------------------------
Traceback (most recent call last):
…
AssertionError: -20 != 0

----------------------------------------------------------------------
Ran 9 tests in 0.001s

FAILED (failures=1)
$ python -m unittest -v
test_book_on_loan_cannot_be_borrowed_again (test_borrow.BorrowTest.test_book_on_loan_cannot_be_borrowed_again) ... ok
test_borrowed_book_is_on_loan (test_borrow.BorrowTest.test_borrowed_book_is_on_loan) ... ok
test_returned_book_is_no_longer_on_loan (test_borrow.BorrowTest.test_returned_book_is_no_longer_on_loan) ... ok
test_early_return_is_free (test_fine.FineTest.test_early_return_is_free) ... ok
test_give_back_returns_the_fine (test_fine.FineTest.test_give_back_returns_the_fine) ... ok
test_return_on_due_date_is_free (test_fine.FineTest.test_return_on_due_date_is_free) ... ok
test_three_days_late_costs_15_taka (test_fine.FineTest.test_three_days_late_costs_15_taka) ... ok
test_due_date_itself_is_not_overdue (test_report.OverdueTest.test_due_date_itself_is_not_overdue) ... ok
test_lists_only_overdue_books_sorted (test_report.OverdueTest.test_lists_only_overdue_books_sorted) ... ok

----------------------------------------------------------------------
Ran 9 tests in 0.000s

OK
$ git add lending.py test_fine.py
$ git commit -m "fix(fine): never charge a negative fine" -m "An early return gave a negative fine since the days_late refactor." -m "Fixes #7"
[fix/negative-fine da9e35e] fix(fine): never charge a negative fine
 2 files changed, 4 insertions(+), 1 deletion(-)
$ git add CHANGELOG.md
$ git commit -m "chore(release): 1.0.1"
[fix/negative-fine 5b3fc4f] chore(release): 1.0.1
 1 file changed, 5 insertions(+)
$ git push -u origin fix/negative-fine
To ../origin.git
 * [new branch]      fix/negative-fine -> fix/negative-fine
branch 'fix/negative-fine' set up to track 'origin/fix/negative-fine'.
$ git switch main
Switched to branch 'main'
Your branch is up to date with 'origin/main'.
$ git pull
Already up to date.
$ git merge --no-ff fix/negative-fine -m "Merge pull request #8 from fix/negative-fine"
Merge made by the 'ort' strategy.
 CHANGELOG.md | 5 +++++
 lending.py   | 2 +-
 test_fine.py | 3 +++
 3 files changed, 9 insertions(+), 1 deletion(-)
$ git tag -a v1.0.1 -m "lending 1.0.1"
$ git push --follow-tags
To ../origin.git
   60c8dab..60b78d1  main -> main
 * [new tag]         v1.0.1 -> v1.0.1
$ git branch -d fix/negative-fine
Deleted branch fix/negative-fine (was 5b3fc4f).
$ git push origin --delete fix/negative-fine
To ../origin.git
 - [deleted]         fix/negative-fine

$ git describe
v1.0.1
$ git describe 5b3fc4f
v1.0.0-2-g5b3fc4f
$ git describe 72cb901
fatal: No tags can describe '72cb9012a7b9866d170d303871dc1682b2b4ccaa'.
Try --always, or create some tags.
$ git describe --contains 72cb901
v1.0.0~2^2~1
$ git tag --contains 72cb901
v1.0.0
v1.0.1

$ git shortlog -sn HEAD
    15	Rahim
     5	Nasrin
$ git shortlog -sn --no-merges HEAD
    10	Rahim
     3	Nasrin
$ git log --format="%h %an %ad %s" --date=iso-strict --reverse
a323299 Rahim 2026-02-01T10:00:00+06:00 chore: initial project skeleton
4a99fdc Rahim 2026-02-01T10:20:00+06:00 ci: add lint and test workflow
86970bb Rahim 2026-02-02T11:00:00+06:00 feat(borrow): borrow and return books
e311026 Rahim 2026-02-04T09:30:00+06:00 test(borrow): reject borrowing a book that is on loan
63acace Rahim 2026-02-04T10:10:00+06:00 Merge pull request #1 from feature/borrow
cadacb4 Nasrin 2026-02-03T12:00:00+06:00 feat(fine): charge 5 taka per late day
4db12a0 Nasrin 2026-02-04T14:40:00+06:00 feat(fine): return the fine from give_back
609f70f Nasrin 2026-02-05T10:15:00+06:00 Merge pull request #2 from feature/fine
63bd2c0 Rahim 2026-02-09T11:00:00+06:00 feat(report): list overdue loans
1bebbf6 Rahim 2026-02-09T14:30:00+06:00 Merge pull request #3 from feature/overdue
72cb901 Rahim 2026-02-10T10:30:00+06:00 refactor(lending): extract days_late helper
1f8d3cb Rahim 2026-02-10T11:00:00+06:00 test(report): cover the due-date boundary
af97afe Rahim 2026-02-11T09:40:00+06:00 Merge pull request #4 from refactor/days-late
27ca69e Nasrin 2026-02-11T10:00:00+06:00 docs(readme): add a usage example
516d42b Nasrin 2026-02-11T11:00:00+06:00 Merge pull request #5 from docs/usage
1aee4eb Rahim 2026-02-12T10:00:00+06:00 chore(release): 1.0.0
60c8dab Rahim 2026-02-12T10:40:00+06:00 Merge pull request #6 from release/1.0.0
da9e35e Rahim 2026-02-15T10:00:00+06:00 fix(fine): never charge a negative fine
5b3fc4f Rahim 2026-02-15T10:10:00+06:00 chore(release): 1.0.1
60b78d1 Rahim 2026-02-15T10:50:00+06:00 Merge pull request #8 from fix/negative-fine

// Retrospective metrics. Commit and merge times are REAL (git log --date=iso-strict);
// PR "opened" and "first review" times are STATED from the fictional PR page (Git keeps no PRs).
const T = s => Date.parse(s + ":00+06:00");
const PRS = [ // [#, first commit, PR opened, first review, merge commit]
  [1, "2026-02-02T11:00", "2026-02-02T11:05", "2026-02-03T15:00", "2026-02-04T10:10"],
  [2, "2026-02-03T12:00", "2026-02-03T12:05", "2026-02-04T11:00", "2026-02-05T10:15"],
  [3, "2026-02-09T11:00", "2026-02-09T11:05", "2026-02-09T14:00", "2026-02-09T14:30"],
  [4, "2026-02-10T10:30", "2026-02-10T11:05", "2026-02-11T09:30", "2026-02-11T09:40"],
  [5, "2026-02-11T10:00", "2026-02-11T10:05", "2026-02-11T10:50", "2026-02-11T11:00"],
  [6, "2026-02-12T10:00", "2026-02-12T10:05", "2026-02-12T10:30", "2026-02-12T10:40"],
  [8, "2026-02-15T10:00", "2026-02-15T10:15", "2026-02-15T10:40", "2026-02-15T10:50"],
];
const h = ms => (ms / 3.6e6).toFixed(1) + "h";
const median = a => { const s = [...a].sort((x, y) => x - y), m = s.length >> 1;
  return s.length % 2 ? s[m] : (s[m - 1] + s[m]) / 2; };
const lead = [], wait = [];
for (const [n, first, open, review, merged] of PRS) {
  lead.push(T(merged) - T(first)); wait.push(T(review) - T(open));
  console.log(`PR #${n}  lead ${h(T(merged) - T(first)).padStart(5)}  review wait ` +
    `${h(T(review) - T(open)).padStart(5)}  open->merge ${h(T(merged) - T(open)).padStart(5)}`);
}
console.log(`median lead ${h(median(lead))} | median review wait ${h(median(wait))}`);
// DORA-style numbers; a release (tag) stands in for a deployment.
const REL = { "v1.0.0": T("2026-02-12T10:45"), "v1.0.1": T("2026-02-15T10:55") };
const CHANGES = [ // author time of every non-merge commit -> first tag that contains it
  ["2026-02-01T10:00", "v1.0.0"], ["2026-02-01T10:20", "v1.0.0"], ["2026-02-02T11:00", "v1.0.0"],
  ["2026-02-04T09:30", "v1.0.0"], ["2026-02-03T12:00", "v1.0.0"], ["2026-02-04T14:40", "v1.0.0"],
  ["2026-02-09T11:00", "v1.0.0"], ["2026-02-10T10:30", "v1.0.0"], ["2026-02-10T11:00", "v1.0.0"],
  ["2026-02-11T10:00", "v1.0.0"], ["2026-02-12T10:00", "v1.0.0"],
  ["2026-02-15T10:00", "v1.0.1"], ["2026-02-15T10:10", "v1.0.1"]];
const lt = CHANGES.map(([t, tag]) => REL[tag] - T(t));
const days = (REL["v1.0.1"] - T("2026-02-01T10:00")) / 864e5;
console.log(`releases 2 in ${days.toFixed(1)} days = ${(2 / days * 7).toFixed(2)} per week`);
console.log(`lead time for changes: median ${h(median(lt))}, max ${h(Math.max(...lt))}`);
console.log(`change failure rate 1/2 = 50% | time to restore ${h(REL["v1.0.1"] - T("2026-02-15T09:00"))}`);

// Burndown and velocity for two 5-day sprints (Sunday-Thursday).
// Story points are STATED planning data. A story counts as done on the day its PR
// was merged (same dates as the commit log): PR #1 on day 4, PR #2 on day 5, PR #3 on day 2.
const SPRINTS = [
  { name: "Sprint 1 (Feb 1-5)",  points: { S1: 3, S2: 2, S3: 1, S4: 5 },
    doneOn: { S1: 4, S2: 4, S3: 4, S4: 5 } },
  { name: "Sprint 2 (Feb 8-12)", points: { S5: 3, S6: 3 },
    doneOn: { S5: 2 } },                     // S6 was not finished
];
const DAYS = 5, velocity = [];
for (const sp of SPRINTS) {
  const total = Object.values(sp.points).reduce((a, b) => a + b, 0);
  console.log(`${sp.name}: committed ${total} points`);
  let left = total;
  for (let d = 1; d <= DAYS; d++) {
    for (const [s, day] of Object.entries(sp.doneOn)) if (day === d) left -= sp.points[s];
    const ideal = total * (1 - d / DAYS);
    console.log(`  day ${d}  left ${String(left).padStart(2)}  ideal ${ideal.toFixed(1).padStart(4)}  ` +
      "#".repeat(left) + (left > ideal ? "   (behind ideal)" : ""));
  }
  const done = total - left;
  velocity.push(done);
  console.log(`  velocity ${done}, commitment kept ${Math.round(100 * done / total)}%`);
}
const mean = velocity.reduce((a, b) => a + b, 0) / velocity.length;
const backlog = 3 + 5;                       // S6 (3) + a new story estimated at 5
console.log(`mean velocity ${mean.toFixed(1)} -> backlog ${backlog} points needs ` +
  `about ${Math.ceil(backlog / mean)} sprint(s); range ${Math.ceil(backlog / Math.max(...velocity))}` +
  `-${Math.ceil(backlog / Math.min(...velocity))} using best and worst sprint`);