comm: implement --total

tests/by-util/test_comm.rs

@@ -55,6 +55,22 @@ fn empty_empty() {
         .stdout_only_fixture("emptyempty.expected"); // spell-checker:disable-line
 }
 
+#[test]
+fn total() {
+    new_ucmd!()
+        .args(&["--total", "a", "b"])
+        .succeeds()
+        .stdout_is_fixture("ab_total.expected");
+}
+
+#[test]
+fn total_with_suppressed_regular_output() {
+    new_ucmd!()
+        .args(&["--total", "-123", "a", "b"])
+        .succeeds()
+        .stdout_is_fixture("ab_total_suppressed_regular_output.expected");
+}
+
 #[test]
 fn output_delimiter() {
     new_ucmd!()

tests/fixtures/comm/ab_total.expected

@@ -0,0 +1,4 @@
+a
+	b
+		z
+1	1	1	total

tests/fixtures/comm/ab_total_suppressed_regular_output.expected

@@ -0,0 +1 @@
+1	1	1	total