diff --git a/tests/by-util/test_cksum.rs b/tests/by-util/test_cksum.rs
index b73ee1425d..64c61cda29 100644
--- a/tests/by-util/test_cksum.rs
+++ b/tests/by-util/test_cksum.rs
@@ -1284,6 +1284,18 @@ fn test_several_files_error_mgmt() {
         .stderr_contains("incorrect: no properly ");
 }
 
+#[test]
+fn test_check_unknown_checksum_file() {
+    let scene = TestScenario::new(util_name!());
+
+    scene
+        .ucmd()
+        .arg("--check")
+        .arg("missing")
+        .fails()
+        .stderr_only("cksum: missing: No such file or directory\n");
+}
+
 #[test]
 fn test_check_comment_line() {
     // A comment in a checksum file shall be discarded unnoticed.
@@ -1811,6 +1823,374 @@ mod gnu_cksum_base64 {
     }
 }
 
+/// This module reimplements the cksum-c.sh GNU test.
+mod gnu_cksum_c {
+    use super::*;
+
+    const INVALID_SUM: &str = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaafdb57c725157cb40b5aee8d937b8351477e";
+
+    fn make_scene() -> TestScenario {
+        let scene = TestScenario::new(util_name!());
+        let at = &scene.fixtures;
+        at.write("input", "9\n7\n1\n4\n2\n6\n3\n5\n8\n10\n");
+
+        let algos: &[&[&str]] = &[
+            &["-a", "sha384"],
+            &["-a", "blake2b"],
+            &["-a", "blake2b", "-l", "384"],
+            &["-a", "sm3"],
+        ];
+
+        for args in algos {
+            let result = scene.ucmd().args(args).succeeds();
+            let stdout = result.stdout();
+            at.append_bytes("CHECKSUMS", stdout);
+        }
+
+        scene
+    }
+
+    #[test]
+    #[ignore]
+    fn test_signed_checksums() {
+        todo!()
+    }
+
+    #[test]
+    fn test_check_individual_digests_in_mixed_file() {
+        let scene = make_scene();
+
+        scene
+            .ucmd()
+            .arg("--check")
+            .arg("-a")
+            .arg("sm3")
+            .arg("CHECKSUMS")
+            .succeeds();
+    }
+
+    #[test]
+    fn test_check_against_older_non_hex_formats() {
+        let scene = make_scene();
+
+        scene
+            .ucmd()
+            .arg("-c")
+            .arg("-a")
+            .arg("crc")
+            .arg("CHECKSUMS")
+            .fails();
+
+        let crc_cmd = scene.ucmd().arg("-a").arg("crc").arg("input").succeeds();
+        let crc_cmd_out = crc_cmd.stdout();
+        scene.fixtures.write_bytes("CHECKSUMS.crc", crc_cmd_out);
+
+        scene.ucmd().arg("-c").arg("CHECKSUMS.crc").fails();
+    }
+
+    #[test]
+    fn test_status() {
+        let scene = make_scene();
+
+        scene
+            .ucmd()
+            .arg("--status")
+            .arg("--check")
+            .arg("CHECKSUMS")
+            .succeeds()
+            .no_output();
+    }
+
+    fn make_scene_with_comment() -> TestScenario {
+        let scene = make_scene();
+
+        scene
+            .fixtures
+            .append("CHECKSUMS", "# Very important comment\n");
+
+        scene
+    }
+
+    #[test]
+    fn test_status_with_comment() {
+        let scene = make_scene_with_comment();
+
+        scene
+            .ucmd()
+            .arg("--status")
+            .arg("--check")
+            .arg("CHECKSUMS")
+            .succeeds()
+            .no_output();
+    }
+
+    fn make_scene_with_invalid_line() -> TestScenario {
+        let scene = make_scene_with_comment();
+
+        scene.fixtures.append("CHECKSUMS", "invalid_line\n");
+
+        scene
+    }
+
+    #[test]
+    fn test_check_strict() {
+        let scene = make_scene_with_invalid_line();
+
+        // without strict, succeeds
+        scene
+            .ucmd()
+            .arg("--check")
+            .arg("CHECKSUMS")
+            .succeeds()
+            .stderr_contains("1 line is improperly formatted");
+
+        // with strict, fails
+        scene
+            .ucmd()
+            .arg("--strict")
+            .arg("--check")
+            .arg("CHECKSUMS")
+            .fails()
+            .stderr_contains("1 line is improperly formatted");
+    }
+
+    fn make_scene_with_two_invalid_lines() -> TestScenario {
+        let scene = make_scene_with_comment();
+
+        scene
+            .fixtures
+            .append("CHECKSUMS", "invalid_line\ninvalid_line\n");
+
+        scene
+    }
+
+    #[test]
+    fn test_check_strict_plural_checks() {
+        let scene = make_scene_with_two_invalid_lines();
+
+        scene
+            .ucmd()
+            .arg("--strict")
+            .arg("--check")
+            .arg("CHECKSUMS")
+            .fails()
+            .stderr_contains("2 lines are improperly formatted");
+    }
+
+    fn make_scene_with_incorrect_checksum() -> TestScenario {
+        let scene = make_scene_with_two_invalid_lines();
+
+        scene
+            .fixtures
+            .append("CHECKSUMS", &format!("SM3 (input) = {INVALID_SUM}\n"));
+
+        scene
+    }
+
+    #[test]
+    fn test_check_with_incorrect_checksum() {
+        let scene = make_scene_with_incorrect_checksum();
+
+        scene
+            .ucmd()
+            .arg("--check")
+            .arg("CHECKSUMS")
+            .fails()
+            .stdout_contains("input: FAILED")
+            .stderr_contains("1 computed checksum did NOT match");
+
+        // also fails with strict
+        scene
+            .ucmd()
+            .arg("--strict")
+            .arg("--check")
+            .arg("CHECKSUMS")
+            .fails()
+            .stdout_contains("input: FAILED")
+            .stderr_contains("1 computed checksum did NOT match");
+    }
+
+    #[test]
+    fn test_status_with_errors() {
+        let scene = make_scene_with_incorrect_checksum();
+
+        scene
+            .ucmd()
+            .arg("--status")
+            .arg("--check")
+            .arg("CHECKSUMS")
+            .fails()
+            .no_output();
+    }
+
+    #[test]
+    fn test_check_with_non_existing_file() {
+        let scene = make_scene();
+        scene
+            .fixtures
+            .write("CHECKSUMS2", &format!("SM3 (input2) = {INVALID_SUM}\n"));
+
+        scene
+            .ucmd()
+            .arg("--check")
+            .arg("CHECKSUMS2")
+            .fails()
+            .stdout_contains("input2: FAILED open or read")
+            .stderr_contains("1 listed file could not be read");
+
+        // also fails with strict
+        scene
+            .ucmd()
+            .arg("--strict")
+            .arg("--check")
+            .arg("CHECKSUMS2")
+            .fails()
+            .stdout_contains("input2: FAILED open or read")
+            .stderr_contains("1 listed file could not be read");
+    }
+
+    fn make_scene_with_another_improperly_formatted() -> TestScenario {
+        let scene = make_scene_with_incorrect_checksum();
+
+        scene.fixtures.append(
+            "CHECKSUMS",
+            &format!("BLAKE2b (missing-file) = {INVALID_SUM}\n"),
+        );
+
+        scene
+    }
+
+    #[test]
+    fn test_warn() {
+        let scene = make_scene_with_another_improperly_formatted();
+
+        scene
+            .ucmd()
+            .arg("--warn")
+            .arg("--check")
+            .arg("CHECKSUMS")
+            .run()
+            .stderr_contains("CHECKSUMS: 6: improperly formatted SM3 checksum line")
+            .stderr_contains("CHECKSUMS: 9: improperly formatted BLAKE2b checksum line");
+    }
+
+    fn make_scene_with_checksum_missing() -> TestScenario {
+        let scene = make_scene_with_another_improperly_formatted();
+
+        scene.fixtures.write(
+            "CHECKSUMS-missing",
+            &format!("SM3 (nonexistent) = {INVALID_SUM}\n"),
+        );
+
+        scene
+    }
+
+    #[test]
+    fn test_ignore_missing() {
+        let scene = make_scene_with_checksum_missing();
+
+        scene
+            .ucmd()
+            .arg("--ignore-missing")
+            .arg("--check")
+            .arg("CHECKSUMS-missing")
+            .fails()
+            .stdout_does_not_contain("nonexistent: No such file or directory")
+            .stdout_does_not_contain("nonexistent: FAILED open or read")
+            .stderr_contains("CHECKSUMS-missing: no file was verified");
+    }
+
+    #[test]
+    fn test_status_and_warn() {
+        let scene = make_scene_with_checksum_missing();
+
+        // --status before --warn
+        scene
+            .ucmd()
+            .arg("--status")
+            .arg("--warn")
+            .arg("--check")
+            .arg("CHECKSUMS")
+            .fails()
+            .stderr_contains("CHECKSUMS: 9: improperly formatted BLAKE2b checksum line")
+            .stderr_contains("WARNING: 3 lines are improperly formatted")
+            .stderr_contains("WARNING: 1 computed checksum did NOT match");
+
+        // --warn before --status (status hides the results)
+        scene
+            .ucmd()
+            .arg("--warn")
+            .arg("--status")
+            .arg("--check")
+            .arg("CHECKSUMS")
+            .fails()
+            .stderr_does_not_contain("CHECKSUMS: 9: improperly formatted BLAKE2b checksum line")
+            .stderr_does_not_contain("WARNING: 3 lines are improperly formatted")
+            .stderr_does_not_contain("WARNING: 1 computed checksum did NOT match");
+    }
+
+    #[test]
+    fn test_status_and_ignore_missing() {
+        let scene = make_scene_with_checksum_missing();
+
+        scene
+            .ucmd()
+            .arg("--status")
+            .arg("--ignore-missing")
+            .arg("--check")
+            .arg("CHECKSUMS")
+            .run()
+            .no_output()
+            .code_is(1);
+    }
+
+    #[test]
+    fn test_status_warn_and_ignore_missing() {
+        let scene = make_scene_with_checksum_missing();
+
+        scene
+            .ucmd()
+            .arg("--status")
+            .arg("--warn")
+            .arg("--ignore-missing")
+            .arg("--check")
+            .arg("CHECKSUMS-missing")
+            .fails()
+            .stderr_contains("CHECKSUMS-missing: no file was verified")
+            .stdout_does_not_contain("nonexistent: No such file or directory");
+    }
+
+    #[test]
+    fn test_check_several_files_dont_exist() {
+        let scene = make_scene();
+
+        scene
+            .ucmd()
+            .arg("--check")
+            .arg("non-existing-1")
+            .arg("non-existing-2")
+            .fails()
+            .stderr_contains("non-existing-1: No such file or directory")
+            .stderr_contains("non-existing-2: No such file or directory");
+    }
+
+    #[test]
+    fn test_check_several_files_empty() {
+        let scene = make_scene();
+        scene.fixtures.touch("empty-1");
+        scene.fixtures.touch("empty-2");
+
+        scene
+            .ucmd()
+            .arg("--check")
+            .arg("empty-1")
+            .arg("empty-2")
+            .fails()
+            .stderr_contains("empty-1: no properly formatted checksum lines found")
+            .stderr_contains("empty-2: no properly formatted checksum lines found");
+    }
+}
+
 /// The tests in this module check the behavior of cksum when given different
 /// checksum formats and algorithms in the same file, while specifying an
 /// algorithm on CLI or not.