fmt: add basic tests for split-only, prefix, and skip-prefix args

tests/by-util/test_fmt.rs

@@ -185,3 +185,87 @@ fn test_fmt_set_goal_not_contain_width() {
             .stdout_is("this is a file with one word per line\n");
     }
 }
+
+#[test]
+fn split_does_not_reflow() {
+    for arg in ["-s", "-ss", "--split-only"] {
+        let (at, mut ucmd) = at_and_ucmd!();
+        ucmd.arg("one-word-per-line.txt")
+            .arg(arg)
+            .succeeds()
+            .stdout_is(at.read("one-word-per-line.txt"));
+    }
+}
+
+#[test]
+fn prefix_minus() {
+    for invocation in [
+        vec!["-p-", "prefixed-one-word-per-line.txt"],
+        vec!["-p", "-", "prefixed-one-word-per-line.txt"],
+        vec!["--prefix=-", "prefixed-one-word-per-line.txt"],
+        vec!["--prefix", "-", "prefixed-one-word-per-line.txt"],
+        vec!["--pref=-", "prefixed-one-word-per-line.txt"],
+        vec!["--pref", "-", "prefixed-one-word-per-line.txt"],
+        // Test self-overriding:
+        vec!["--prefix==", "--prefix=-", "prefixed-one-word-per-line.txt"],
+    ] {
+        let (at, mut ucmd) = at_and_ucmd!();
+        ucmd.args(&invocation)
+            .succeeds()
+            .stdout_is(at.read("prefixed-one-word-per-line_p-.txt"));
+    }
+}
+
+#[test]
+fn prefix_equal() {
+    for invocation in [
+        // FIXME: #6353 vec!["-p=", "prefixed-one-word-per-line.txt"],
+        vec!["-p", "=", "prefixed-one-word-per-line.txt"],
+        vec!["--prefix==", "prefixed-one-word-per-line.txt"],
+        vec!["--prefix", "=", "prefixed-one-word-per-line.txt"],
+        vec!["--pref==", "prefixed-one-word-per-line.txt"],
+        vec!["--pref", "=", "prefixed-one-word-per-line.txt"],
+        // Test self-overriding:
+        vec!["--prefix=-", "--prefix==", "prefixed-one-word-per-line.txt"],
+    ] {
+        let (at, mut ucmd) = at_and_ucmd!();
+        ucmd.args(&invocation)
+            .succeeds()
+            .stdout_is(at.read("prefixed-one-word-per-line_p=.txt"));
+    }
+}
+
+#[test]
+fn prefix_equal_skip_prefix_equal_two() {
+    for invocation in [
+        // FIXME: #6353 vec!["--prefix==", "-P=2", "prefixed-one-word-per-line.txt"],
+        vec!["--prefix==", "-P", "=2", "prefixed-one-word-per-line.txt"],
+        vec![
+            "--prefix==",
+            "--skip-prefix==2",
+            "prefixed-one-word-per-line.txt",
+        ],
+        vec![
+            "--prefix==",
+            "--skip-prefix",
+            "=2",
+            "prefixed-one-word-per-line.txt",
+        ],
+        vec![
+            "--prefix==",
+            "--skip-pref==2",
+            "prefixed-one-word-per-line.txt",
+        ],
+        vec![
+            "--prefix==",
+            "--skip-pref",
+            "=2",
+            "prefixed-one-word-per-line.txt",
+        ],
+    ] {
+        let (at, mut ucmd) = at_and_ucmd!();
+        ucmd.args(&invocation)
+            .succeeds()
+            .stdout_is(at.read("prefixed-one-word-per-line_p=_P=2.txt"));
+    }
+}