3 files changed, 22 insertions, 0 deletions
diff --git a/tests/function.err b/tests/function.err
index e69de29b..72671ac9 100644
--- a/tests/function.err
+++ b/tests/function.err
@@ -0,0 +1,8 @@
+function: function name shadows a builtin so you must use '--shadow-builtin'
+fish: function pwd; end
+      ^
+yes, it failed as expected
+function: function name does not shadow a builtin so you must not use '--shadow-builtin'
+fish: function not_builtin --shadow-builtin; end
+      ^
+yes, it failed as expected
diff --git a/tests/function.in b/tests/function.in
index 747bbcec..8202fb13 100644
--- a/tests/function.in
+++ b/tests/function.in
@@ -44,3 +44,16 @@ for i in (seq 4)
         echo "Function name$i not found, but should have been"
     end
 end
+
+# Test that we can't define a function that shadows a builtin by accident.
+function pwd; end
+or echo 'yes, it failed as expected' >&2
+
+# Test that we can define a function that shadows a builtin if we use the
+# right flag.
+function pwd --shadow-builtin; end
+and echo '"function pwd --shadow-builtin" worked'
+
+# Using --shadow-builtin for a non-builtin function name also fails.
+function not_builtin --shadow-builtin; end
+or echo 'yes, it failed as expected' >&2
diff --git a/tests/function.out b/tests/function.out
index 5a3da619..0d12479e 100644
--- a/tests/function.out
+++ b/tests/function.out
@@ -22,3 +22,4 @@ Function name1 found
 Function name2 found
 Function name3 found
 Function name4 found
+"function pwd --shadow-builtin" worked