How can I see the git history of a deleted branch (used git flow)

Question

Looks like you merged branch A into develop first at 7a0ad6b. Not quite sure what happened after that. According to your git log output, it looks like you might have merged B into develop at e553bf0:

* | |   e553bf0 resolved merge conflicts
|\ \ \  
| * | | 6b30050 fixed test db error
| * | |   64909f9 Merge branch 'develop' into feature/b

But according to your reflog, 6b30050 is actually feature/a:

6b30050 HEAD@{43}: checkout: moving from develop to feature/a
e553bf0 HEAD@{44}: commit (merge): resolved merge conflicts

You didn't accidentally get the branch names mixed up when you were copying the output into your question, did you?

Looking at just the reflog

Based on your original reflog alone, it looks like you merged branch B into develop first, then tried to merge branch A, resolved conflicts, then committed:

# Checkout develop
e553bf0 HEAD@{42}: checkout: moving from feature/a to develop

# Checkout branch A
6b30050 HEAD@{43}: checkout: moving from develop to feature/a

# Merge branch A? Resolve conflicts and commit
e553bf0 HEAD@{44}: commit (merge): resolved merge conflicts

# Checkout develop
7a0ad6b HEAD@{45}: checkout: moving from feature/a to develop

# Checkout branch A
6b30050 HEAD@{46}: checkout: moving from develop to feature/a

# Merge branch B into develop
7a0ad6b HEAD@{47}: merge feature/b: Merge made by the 'recursive' strategy.

# Move from branch B to develop (i.e. checkout commit 921ae46)
921ae46 HEAD@{48}: checkout: moving from feature/b to develop

Viewing the history of the merged branch

When you figure out which merge is which, you should be able to view the log of the branch by using

git log --oneline --graph <sha of merge into develop>^2

which means show the history of the 2nd parent of the merge commit, which will be the tip of the feature branch if you're using git flow.

If it helps, you can also view the history of the develop branch with both the authored date and commit-date using this alias in your user .gitconfig file:

[alias]
    datelog = log --format=\"%C(yellow)%h%C(reset) %C(cyan dim)%ad %C(red bold)%cd %C(reset)%s\" --graph

It will show you the authored date first in blue, then the commit-date in red. Using the commit-date, you might be able to figure out if branch A or B was merged into develop first. You can also get both authored and commit-dates using git log --format=fuller.

Favor rebase over merge (usually)

Finally, do you know how to rebase? You can avoid polluting your branch histories with sync/merge commits with develop by using rebase to sync instead of merge:

# From feature branch X, sync with develop
git rebase develop

# Switch to develop and merge
# (either fast-forward or merge commit, your choice)
git checkout develop
git merge --no-ff X