t2018: move checkout case-insensitive test from t0050

The test 'checkout with no pathspec and a case insensitive fs' in
t0050 does not really belong there as it tests branch checkout
behavior, not filesystem properties.  It also had an unnecessary
CASE_INSENSITIVE_FS prereq since the sequence of commands should
succeed on any filesystem, and it did not verify the resulting
worktree contents.

Move it to t2018-checkout-branch.sh where it belongs, drop the
prereq, and add a check that the expected file is present after
the checkout.

Signed-off-by: mdferdousalam <mdferdousalam1989@yahoo.com>

Author: mdferdousalam

t/t0050-filesystem.sh

@@ -117,24 +117,4 @@ $test_unicode 'merge (silent unicode normalization)' '
 	git merge topic
 '
 
-test_expect_success CASE_INSENSITIVE_FS 'checkout with no pathspec and a case insensitive fs' '
-	git init repo &&
-	(
-		cd repo &&
-
-		>Gitweb &&
-		git add Gitweb &&
-		git commit -m "add Gitweb" &&
-
-		git checkout --orphan todo &&
-		git reset --hard &&
-		mkdir -p gitweb/subdir &&
-		>gitweb/subdir/file &&
-		git add gitweb &&
-		git commit -m "add gitweb/subdir/file" &&
-
-		git checkout main
-	)
-'
-
 test_done

t/t2018-checkout-branch.sh

@@ -285,4 +285,25 @@ test_expect_success 'checkout -b rejects an extra path argument' '
 	test_grep "Cannot update paths and switch to branch" err
 '
 
+test_expect_success 'checkout a branch when file and directory share case-insensitive name' '
+	git init repo-case &&
+	(
+		cd repo-case &&
+
+		>Gitweb &&
+		git add Gitweb &&
+		git commit -m "add Gitweb" &&
+
+		git checkout --orphan other &&
+		git reset --hard &&
+		mkdir -p gitweb/subdir &&
+		>gitweb/subdir/file &&
+		git add gitweb &&
+		git commit -m "add gitweb/subdir/file" &&
+
+		git checkout master &&
+		test_path_is_file Gitweb
+	)
+'
+
 test_done