diff --git a/tests/comm.rs b/tests/comm.rs
index 390d50b89..14ff0c726 100644
--- a/tests/comm.rs
+++ b/tests/comm.rs
@@ -1,47 +1,166 @@
-#[macro_use] mod common;
-
-use common::util;
+#[macro_use]
+mod common;
 
+use common::util::testing;
+use std::ffi::OsStr;
 static UTIL_NAME: &'static str = "comm";
 
-#[test]
-fn test_comm_ab_no_args() {
-    let (at, mut ucmd) = util::testing(UTIL_NAME);
-    let result = ucmd.args(&["a", "b"]).run();
-    assert_eq!(result.stdout, at.read("ab.expected"));
+fn comm<A: AsRef<OsStr>, B: AsRef<str>>(args: &[A],
+                                                       file_stdout_relpath_opt: Option<B>,
+                                                       error_message_opt: Option<B>) {
+    let (at, mut ucmd) = testing(UTIL_NAME);
+    let result = ucmd.args(args)
+                     .run();
+    assert!(result.success == error_message_opt.is_none());
+    if let Some(_) = error_message_opt {
+        assert!(result.stderr.len() > 0);
+        // assert!(result.stderr.trim_right() == s);
+    } else {
+        assert!(result.stderr.len() == 0);
+    }
+    if let Some(file_stdout_relpath) = file_stdout_relpath_opt {
+        assert!(result.stdout == at.read(file_stdout_relpath.as_ref()))
+    }
 }
 
 #[test]
-fn test_comm_ab_dash_one() {
-    let (at, mut ucmd) = util::testing(UTIL_NAME);
-    let result = ucmd.args(&["a", "b", "-1"]).run();
-    assert_eq!(result.stdout, at.read("ab1.expected"));
+fn ab_no_args() {
+    comm(&["a", "b"], Some("ab.expected"), None);
 }
 
 #[test]
-fn test_comm_ab_dash_two() {
-    let (at, mut ucmd) = util::testing(UTIL_NAME);
-    let result = ucmd.args(&["a", "b", "-2"]).run();
-    assert_eq!(result.stdout, at.read("ab2.expected"));
+fn ab_dash_one() {
+    comm(&["a", "b", "-1"], Some("ab1.expected"), None);
 }
 
 #[test]
-fn test_comm_ab_dash_three() {
-    let (at, mut ucmd) = util::testing(UTIL_NAME);
-    let result = ucmd.args(&["a", "b", "-3"]).run();
-    assert_eq!(result.stdout, at.read("ab3.expected"));
+fn ab_dash_two() {
+    comm(&["a", "b", "-2"], Some("ab2.expected"), None);
 }
 
 #[test]
-fn test_comm_aempty() {
-    let (at, mut ucmd) = util::testing(UTIL_NAME);
-    let result = ucmd.args(&["a", "empty"]).run();
-    assert_eq!(result.stdout, at.read("aempty.expected"));
+fn ab_dash_three() {
+    comm(&["a", "b", "-3"], Some("ab3.expected"), None);
 }
 
 #[test]
-fn test_comm_emptyempty() {
-    let (at, mut ucmd) = util::testing(UTIL_NAME);
-    let result = ucmd.args(&["empty", "empty"]).run();
-    assert_eq!(result.stdout, at.read("emptyempty.expected"));
+fn aempty() {
+    comm(&["a", "empty"], Some("aempty.expected"), None);
+}
+
+#[test]
+fn emptyempty() {
+    comm(&["empty", "empty"], Some("emptyempty.expected"), None);
+}
+
+#[cfg_attr(not(feature="test_unimplemented"),ignore)]
+#[test]
+fn output_delimiter() {
+    comm(&["--output-delimiter=word", "a", "b"],
+               Some("ab_delimiter_word.expected"),
+               None);
+}
+
+#[cfg_attr(not(feature="test_unimplemented"),ignore)]
+#[test]
+fn output_delimiter_require_arg() {
+    comm(&["--output-delimiter=", "a", "b"],
+               None,
+               Some("error to be defined"));
+}
+
+// even though (info) documentation suggests this is an option
+// in latest GNU Coreutils comm, it actually is not.
+// this test is essentially an alarm in case someone well-intendingly
+// implements it.
+#[test]
+fn zero_terminated() {
+    for param in vec!["-z", "--zero-terminated"] {
+        comm(&[param, "a", "b"], None, Some("error to be defined"));
+    }
+}
+
+#[cfg_attr(not(feature="test_unimplemented"),ignore)]
+#[test]
+fn check_order() {
+    comm(&["--check-order", "bad_order_1", "bad_order_2"],
+               Some("bad_order12.check_order.expected"),
+               Some("error to be defined"));
+}
+
+#[cfg_attr(not(feature="test_unimplemented"),ignore)]
+#[test]
+fn nocheck_order() {
+    comm(&["--nocheck-order", "bad_order_1", "bad_order_2"],
+               Some("bad_order12.nocheck_order.expected"),
+               None);
+}
+
+// when neither --check-order nor --no-check-order is provided,
+// stderr and the error code behaves like check order, but stdout
+// behaves like nocheck_order. However with some quirks detailed below.
+#[cfg_attr(not(feature="test_unimplemented"),ignore)]
+#[test]
+fn defaultcheck_order() {
+    comm(&["a", "bad_order_1"], None, Some("error to be defined"));
+}
+
+// * the first: if both files are not in order, the default behavior is the only
+// behavior that will provide an error message
+
+// * the second: if two rows are paired but are out of order,
+// it won't matter if all rows in the two files are exactly the same.
+// This is specified in the documentation
+
+#[test]
+fn defaultcheck_order_identical_bad_order_files() {
+    comm(&["bad_order_1", "bad_order_1"],
+               Some("bad_order11.defaultcheck_order.expected"),
+               None);
+}
+
+#[cfg_attr(not(feature="test_unimplemented"),ignore)]
+#[test]
+fn defaultcheck_order_two_different_bad_order_files() {
+    comm(&["bad_order_1", "bad_order_2"],
+               Some("bad_order12.nocheck_order.expected"),
+               Some("error to be defined"));
+}
+
+// * the third: (it is not know whether this is a bug or not)
+// for the first incident, and only the first incident,
+// where both lines are different and one or both file lines being
+// compared are out of order from the preceding line,
+// it is ignored and no errors occur.
+
+// * the fourth: (it is not known whether this is a bug or not)
+// there are additional, not-yet-understood circumstances where an out-of-order
+// pair is ignored and is not counted against the 1 maximum out-of-order line.
+
+#[cfg_attr(not(feature="test_unimplemented"),ignore)]
+#[test]
+fn unintuitive_default_behavior_1() {
+    comm(&["defaultcheck_unintuitive_1", "defaultcheck_unintuitive_2"],
+               Some("defaultcheck_unintuitive.expected"),
+               None);
+}
+
+#[ignore] //bug? should help be stdout if not called via -h|--help?
+#[test]
+fn no_arguments() {
+    let (_, mut ucmd) = testing(UTIL_NAME);
+    let result = ucmd.run();
+    assert!(!result.success);
+    assert!(result.stdout.len() == 0);
+    assert!(result.stderr.len() > 0);
+}
+
+#[ignore] //bug? should help be stdout if not called via -h|--help?
+#[test]
+fn one_argument() {
+    let (_, mut ucmd) = testing(UTIL_NAME);
+    let result = ucmd.arg("a").run();
+    assert!(!result.success);
+    assert!(result.stdout.len() == 0);
+    assert!(result.stderr.len() > 0);
 }
diff --git a/tests/fixtures/comm/ab_delimiter_word.expected b/tests/fixtures/comm/ab_delimiter_word.expected
new file mode 100644
index 000000000..a0c510e20
--- /dev/null
+++ b/tests/fixtures/comm/ab_delimiter_word.expected
@@ -0,0 +1,3 @@
+a
+wordb
+wordwordz
diff --git a/tests/fixtures/comm/bad_order11.defaultcheck_order.expected b/tests/fixtures/comm/bad_order11.defaultcheck_order.expected
new file mode 100644
index 000000000..81aa48629
--- /dev/null
+++ b/tests/fixtures/comm/bad_order11.defaultcheck_order.expected
@@ -0,0 +1,4 @@
+		e
+		d
+		b
+		a
diff --git a/tests/fixtures/comm/bad_order12.check_order.expected b/tests/fixtures/comm/bad_order12.check_order.expected
new file mode 100644
index 000000000..3930ff036
--- /dev/null
+++ b/tests/fixtures/comm/bad_order12.check_order.expected
@@ -0,0 +1 @@
+		e
diff --git a/tests/fixtures/comm/bad_order12.nocheck_order.expected b/tests/fixtures/comm/bad_order12.nocheck_order.expected
new file mode 100644
index 000000000..b57118013
--- /dev/null
+++ b/tests/fixtures/comm/bad_order12.nocheck_order.expected
@@ -0,0 +1,7 @@
+		e
+	c
+	b
+	a
+d
+b
+a
diff --git a/tests/fixtures/comm/bad_order_1 b/tests/fixtures/comm/bad_order_1
new file mode 100644
index 000000000..2ebde65a6
--- /dev/null
+++ b/tests/fixtures/comm/bad_order_1
@@ -0,0 +1,4 @@
+e
+d
+b
+a
diff --git a/tests/fixtures/comm/bad_order_2 b/tests/fixtures/comm/bad_order_2
new file mode 100644
index 000000000..76603aede
--- /dev/null
+++ b/tests/fixtures/comm/bad_order_2
@@ -0,0 +1,4 @@
+e
+c
+b
+a
diff --git a/tests/fixtures/comm/defaultcheck_unintuitive.expected b/tests/fixtures/comm/defaultcheck_unintuitive.expected
new file mode 100644
index 000000000..132eab5b2
--- /dev/null
+++ b/tests/fixtures/comm/defaultcheck_unintuitive.expected
@@ -0,0 +1,6 @@
+		m
+		h
+		n
+		o
+c
+		p
diff --git a/tests/fixtures/comm/defaultcheck_unintuitive_1 b/tests/fixtures/comm/defaultcheck_unintuitive_1
new file mode 100644
index 000000000..f32fc1fd7
--- /dev/null
+++ b/tests/fixtures/comm/defaultcheck_unintuitive_1
@@ -0,0 +1,6 @@
+m
+h
+n
+o
+c
+p
diff --git a/tests/fixtures/comm/defaultcheck_unintuitive_2 b/tests/fixtures/comm/defaultcheck_unintuitive_2
new file mode 100644
index 000000000..212de88c4
--- /dev/null
+++ b/tests/fixtures/comm/defaultcheck_unintuitive_2
@@ -0,0 +1,5 @@
+m
+h
+n
+o
+p
diff --git a/tests/fixtures/comm/lowercase_uppercase b/tests/fixtures/comm/lowercase_uppercase
new file mode 100644
index 000000000..768ebc2b9
--- /dev/null
+++ b/tests/fixtures/comm/lowercase_uppercase
@@ -0,0 +1,2 @@
+a
+A
\ No newline at end of file
diff --git a/tests/fixtures/comm/lowercase_uppercase.c.expected b/tests/fixtures/comm/lowercase_uppercase.c.expected
new file mode 100644
index 000000000..8458d7960
--- /dev/null
+++ b/tests/fixtures/comm/lowercase_uppercase.c.expected
@@ -0,0 +1 @@
+		a
diff --git a/tests/fixtures/comm/lowercase_uppercase.en_us.expected b/tests/fixtures/comm/lowercase_uppercase.en_us.expected
new file mode 100644
index 000000000..3992b34d0
--- /dev/null
+++ b/tests/fixtures/comm/lowercase_uppercase.en_us.expected
@@ -0,0 +1,2 @@
+		a
+		A