Documents: \( pairs stay in one paragraph and off addresses; formulas place at wraps

- Pairs pair inside one paragraph, heading or cell; links' addresses,
  images, code and <code>/<kbd> text stay literal.
- Adjacent formulas stay two; a parting space is dropped after parsing.
- Stray and escaped dollars, in or out of a formula, stay dollars.
- A formula's node spans its delimiters; its value is the written TeX.
- A formula wrapped whole draws at its own line's start.
- A failed inline formula shows its reason after the TeX.

Co-Authored-By: Claude <noreply@anthropic.com>

src/documents/markdown/tex/tests.rs

@@ -0,0 +1,99 @@
+use markdown::mdast::Node;
+
+use crate::documents::markdown::{options, span, tree, walk};
+
+/// Each formula's TeX and span, and the text left.
+fn read(source: &str) -> (Vec<(String, std::ops::Range<usize>)>, String) {
+    let root = tree(source);
+    let mut nodes = Vec::new();
+    walk(&root, &mut nodes);
+    let mut maths = Vec::new();
+    let mut text = String::new();
+    for node in nodes {
+        match node {
+            Node::InlineMath(math) => maths.push((math.value.clone(), span(node))),
+            Node::Text(written) => text.push_str(&written.value),
+            _ => {}
+        }
+    }
+    (maths, text)
+}
+
+fn tex(source: &str) -> Vec<String> {
+    read(source).0.into_iter().map(|(tex, _)| tex).collect()
+}
+
+fn untouched(source: &str) {
+    let plain = markdown::to_mdast(source, &options()).unwrap();
+    assert_eq!(tree(source), plain, "{source:?}");
+}
+
+#[test]
+fn a_pair_spans_its_delimiters_and_keeps_its_tex() {
+    assert_eq!(
+        read(r"a \(x\) b"),
+        (vec![("x".into(), 2..7)], "a  b".into())
+    );
+    assert_eq!(tex(r"\( x \)"), [" x "]);
+    assert_eq!(tex(r"\(x \)\(y\)"), ["x ", "y"]);
+}
+
+#[test]
+fn adjacent_formulas_stay_two() {
+    for (source, maths) in [
+        (r"\(x\)\(y\)", vec!["x", "y"]),
+        (r"$x$\(y\)", vec!["x", "y"]),
+        (r"\(y\)$x$", vec!["y", "x"]),
+        (r"\[x\]\(y\)", vec!["x", "y"]),
+    ] {
+        let (found, text) = read(source);
+        let found: Vec<_> = found.into_iter().map(|(tex, _)| tex).collect();
+        assert_eq!(found, maths, "{source:?}");
+        assert_eq!(text, "", "no parting space shows: {source:?}");
+    }
+}
+
+#[test]
+fn dollars_stay_dollars() {
+    assert_eq!(tex(r"\(\$5\)"), [r"\$5"]);
+    assert_eq!(tex(r"\[a \$ b\]"), [r"a \$ b"]);
+    assert_eq!(tex(r"\(a$b\)"), ["a$b"]);
+    assert_eq!(
+        read(r"costs $5 and \(x\)"),
+        (vec![("x".into(), 13..18)], "costs $5 and ".into()),
+        "a stray dollar does not pair with a formula"
+    );
+    assert_eq!(read(r"\$\(x\)").1, "$", "an escaped dollar before");
+    assert_eq!(read(r"\(x\)\$").1, "$", "an escaped dollar after");
+}
+
+#[test]
+fn addresses_keep_their_parentheses() {
+    let link = r"[go](https://e.test/\(x\))";
+    untouched(link);
+    untouched(r"![p](pics/\(x\).png)");
+    untouched("[go][a\\(x\\)]\n\n[a\\(x\\)]: /u");
+    untouched(r"<https://e.test/\(x\)>");
+    assert_eq!(tex(r"[\(x\)](https://e.test)"), ["x"], "link text is prose");
+    untouched(r"[a\(b](c)\)");
+}
+
+#[test]
+fn code_and_tags_stay_literal() {
+    untouched(r"a <code>\(x\)</code> b");
+    untouched(r"a <kbd>\(x\)</kbd> b");
+    untouched(r"a <code>\(x\) b");
+    untouched(r"`\(x\)`");
+    untouched(r"\(a `b` c\)");
+    assert_eq!(tex(r"<b>\(x\)</b>"), ["x"], "other tags hold prose");
+}
+
+#[test]
+fn a_pair_stays_in_one_block() {
+    untouched("- \\(a\n- b\\)");
+    untouched("\\(a\r\rb\\)");
+    untouched("\\(a\r\n\r\nb\\)");
+    untouched("# \\(a\nb\\)");
+    untouched("| \\(a | b\\) |\n| - | - |");
+    assert_eq!(tex("> \\(a\n> b\\)"), ["a\nb"], "a quote's lines");
+}