diff --git a/test/strbuf.carp b/test/strbuf.carp
index 5a244a6..1eeb8df 100644
--- a/test/strbuf.carp
+++ b/test/strbuf.carp
@@ -135,4 +135,24 @@
         (StringBuf.delete sb)
         (StringBuf.delete sb2)
         s))
-    "copy produces independent clone"))
+    "copy produces independent clone")
+
+  (assert-equal test
+    "hello"
+    &(let-do [sb (StringBuf.with-capacity 4)]
+      (StringBuf.append-str &sb "hello")
+      (let-do [s (StringBuf.to-string &sb)] (StringBuf.delete sb) s))
+    "with-capacity grows past initial capacity")
+
+  (assert-equal test
+    0
+    (let [sb (StringBuf.with-capacity 0)]
+      (let-do [l (StringBuf.length &sb)] (StringBuf.delete sb) l))
+    "with-capacity 0 yields an empty buffer")
+
+  (assert-equal test
+    "hello"
+    &(let-do [sb (StringBuf.with-capacity 0)]
+      (StringBuf.append-str &sb "hello")
+      (let-do [s (StringBuf.to-string &sb)] (StringBuf.delete sb) s))
+    "with-capacity 0 buffer grows and is usable"))