test/system: Test 'completion' with two invalid and valid arguments

... in addition to the existing tests for one invalid or valid argument.

This is meant to further ensure that the 'completion' command takes
exactly one positional argument from the ones listed in
cobra.Command.ValidArgs, and as specified by cobra.ExactValidArgs(1).

#1776

Author: debarshiray

test/system/108-completion.bats

@@ -62,7 +62,7 @@ setup() {
   assert [ ${#stderr_lines[@]} -eq 2 ]
 }
 
-@test "completion: Try with invalid arguments" {
+@test "completion: Try with one invalid argument" {
   run --keep-empty-lines --separate-stderr "$TOOLBX" completion foo
 
   assert_failure
@@ -73,6 +73,28 @@ setup() {
   assert [ ${#stderr_lines[@]} -eq 2 ]
 }
 
+@test "completion: Try with two invalid arguments" {
+  run --keep-empty-lines --separate-stderr "$TOOLBX" completion foo bar
+
+  assert_failure
+  assert [ ${#lines[@]} -eq 0 ]
+  lines=("${stderr_lines[@]}")
+  assert_line --index 0 "Error: accepts 1 arg(s), received 2"
+  assert_line --index 1 "Run 'toolbox --help' for usage."
+  assert [ ${#stderr_lines[@]} -eq 2 ]
+}
+
+@test "completion: Try with two valid arguments" {
+  run --keep-empty-lines --separate-stderr "$TOOLBX" completion bash fish
+
+  assert_failure
+  assert [ ${#lines[@]} -eq 0 ]
+  lines=("${stderr_lines[@]}")
+  assert_line --index 0 "Error: accepts 1 arg(s), received 2"
+  assert_line --index 1 "Run 'toolbox --help' for usage."
+  assert [ ${#stderr_lines[@]} -eq 2 ]
+}
+
 @test "completion: Try with unknown flag" {
   run --keep-empty-lines --separate-stderr "$TOOLBX" completion --foo