I first only had master branch.
I then checked out to a new branch using:

git checkout -b install-new-feature

I installed the new feature and then used the command git checkout master, and got the following message:

Switched to branch 'master'
Your branch is up to date with 'origin/master'.

And now I see the changes I made on the install-new-feature branch on master.

I thought git would not allow me to switch to another branch unless I committed the changes made in the modified branch?