diff --git a/src/librustdoc/html/length_limit.rs b/src/librustdoc/html/length_limit.rs
index 2b47033744f..ecf41f7afa7 100644
--- a/src/librustdoc/html/length_limit.rs
+++ b/src/librustdoc/html/length_limit.rs
@@ -98,3 +98,6 @@ impl HtmlWithLimit {
         }
     }
 }
+
+#[cfg(test)]
+mod tests;
diff --git a/src/librustdoc/html/length_limit/tests.rs b/src/librustdoc/html/length_limit/tests.rs
new file mode 100644
index 00000000000..5a006d44d58
--- /dev/null
+++ b/src/librustdoc/html/length_limit/tests.rs
@@ -0,0 +1,117 @@
+use super::*;
+
+#[test]
+fn empty() {
+    assert_eq!(HtmlWithLimit::new(0).finish(), "");
+    assert_eq!(HtmlWithLimit::new(60).finish(), "");
+}
+
+#[test]
+fn basic() {
+    let mut buf = HtmlWithLimit::new(60);
+    buf.push("Hello ");
+    buf.open_tag("em");
+    buf.push("world");
+    buf.close_tag();
+    buf.push("!");
+    assert_eq!(buf.finish(), "Hello <em>world</em>!");
+}
+
+#[test]
+fn no_tags() {
+    let mut buf = HtmlWithLimit::new(60);
+    buf.push("Hello");
+    buf.push(" world!");
+    assert_eq!(buf.finish(), "Hello world!");
+}
+
+#[test]
+fn limit_0() {
+    let mut buf = HtmlWithLimit::new(0);
+    buf.push("Hello ");
+    buf.open_tag("em");
+    buf.push("world");
+    buf.close_tag();
+    buf.push("!");
+    assert_eq!(buf.finish(), "");
+}
+
+#[test]
+fn exactly_limit() {
+    let mut buf = HtmlWithLimit::new(12);
+    buf.push("Hello ");
+    buf.open_tag("em");
+    buf.push("world");
+    buf.close_tag();
+    buf.push("!");
+    assert_eq!(buf.finish(), "Hello <em>world</em>!");
+}
+
+#[test]
+fn multiple_nested_tags() {
+    let mut buf = HtmlWithLimit::new(60);
+    buf.open_tag("p");
+    buf.push("This is a ");
+    buf.open_tag("em");
+    buf.push("paragraph");
+    buf.open_tag("strong");
+    buf.push("!");
+    buf.close_tag();
+    buf.close_tag();
+    buf.close_tag();
+    assert_eq!(buf.finish(), "<p>This is a <em>paragraph<strong>!</strong></em></p>");
+}
+
+#[test]
+fn forgot_to_close_tags() {
+    let mut buf = HtmlWithLimit::new(60);
+    buf.open_tag("p");
+    buf.push("This is a ");
+    buf.open_tag("em");
+    buf.push("paragraph");
+    buf.open_tag("strong");
+    buf.push("!");
+    assert_eq!(buf.finish(), "<p>This is a <em>paragraph<strong>!</strong></em></p>");
+}
+
+#[test]
+fn past_the_limit() {
+    let mut buf = HtmlWithLimit::new(20);
+    buf.open_tag("p");
+    (0..10).try_for_each(|n| {
+        buf.open_tag("strong");
+        buf.push("word#")?;
+        buf.push(&n.to_string())?;
+        buf.close_tag();
+        ControlFlow::CONTINUE
+    });
+    buf.close_tag();
+    assert_eq!(
+        buf.finish(),
+        "<p>\
+             <strong>word#0</strong>\
+             <strong>word#1</strong>\
+             <strong>word#2</strong>\
+             </p>"
+    );
+}
+
+#[test]
+fn quickly_past_the_limit() {
+    let mut buf = HtmlWithLimit::new(6);
+    buf.open_tag("p");
+    buf.push("Hello");
+    buf.push(" World");
+    // intentionally not closing <p> before finishing
+    assert_eq!(buf.finish(), "<p>Hello</p>");
+}
+
+#[test]
+#[should_panic = "called `Option::unwrap()` on a `None` value"]
+fn close_too_many() {
+    let mut buf = HtmlWithLimit::new(60);
+    buf.open_tag("p");
+    buf.push("Hello");
+    buf.close_tag();
+    buf.close_tag();
+}
diff --git a/src/librustdoc/html/markdown/tests.rs b/src/librustdoc/html/markdown/tests.rs
index 1e4bdc2d151..eca75ef013a 100644
--- a/src/librustdoc/html/markdown/tests.rs
+++ b/src/librustdoc/html/markdown/tests.rs
@@ -225,6 +225,7 @@ fn test_short_markdown_summary() {
         assert_eq!(output, expect, "original: {}", input);
     }
 
+    t("", "");
     t("hello [Rust](https://www.rust-lang.org) :)", "hello Rust :)");
     t("*italic*", "<em>italic</em>");
     t("**bold**", "<strong>bold</strong>");
@@ -264,6 +265,7 @@ fn test_plain_text_summary() {
         assert_eq!(output, expect, "original: {}", input);
     }
 
+    t("", "");
     t("hello [Rust](https://www.rust-lang.org) :)", "hello Rust :)");
     t("**bold**", "bold");
     t("Multi-line\nsummary", "Multi-line summary");