Update response handling to add tests for cargo yank --undo

Follow up 5e15286.

crates/crates-io/lib.rs

@@ -298,8 +298,21 @@ impl Registry {
 
     pub fn unyank(&mut self, krate: &str, version: &str) -> Result<()> {
         let body = self.put(&format!("/crates/{}/{}/unyank", krate, version), &[])?;
-        assert!(serde_json::from_str::<R>(&body)?.ok);
-        Ok(())
+        let body = if body.is_empty() {
+            r#"{"ok":false}"#.parse()?
+        } else {
+            body
+        };
+        match serde_json::from_str::<R>(&body) {
+            Ok(response) => {
+                if response.ok {
+                    Ok(())
+                } else {
+                    bail!("ok is false in response body")
+                }
+            }
+            _ => bail!("failed to parse response body"),
+        }
     }
 
     fn put(&mut self, path: &str, b: &[u8]) -> Result<String> {

tests/testsuite/yank.rs

@@ -35,4 +35,17 @@ fn simple() {
     p.cargo("yank --vers 0.0.1 --index")
         .arg(registry_url().to_string())
         .run();
+
+    p.cargo("yank --undo --vers 0.0.1 --index")
+        .arg(registry_url().to_string())
+        .with_status(101)
+        .with_stderr(
+            "    Updating `[..]` index
+      Unyank foo:0.0.1
+error: failed to undo a yank
+
+Caused by:
+  ok is false in response body",
+        )
+        .run();
 }