Add test for building corelib docs (#1687)

extensions/scarb-doc/tests/core.rs

@@ -0,0 +1,23 @@
+use assert_fs::TempDir;
+use scarb_metadata::Metadata;
+use scarb_test_support::command::{CommandExt, Scarb};
+use scarb_test_support::project_builder::ProjectBuilder;
+
+#[test]
+fn can_doc_corelib() {
+    let t = TempDir::new().unwrap();
+    // Find path to corelib.
+    ProjectBuilder::start().name("hello").build(&t);
+    let metadata = Scarb::quick_snapbox()
+        .args(["--json", "metadata", "--format-version", "1"])
+        .current_dir(&t)
+        .stdout_json::<Metadata>();
+    let core = metadata.packages.iter().find(|p| p.name == "core").unwrap();
+    let core = core.root.clone();
+    // Doc corelib.
+    Scarb::quick_snapbox()
+        .arg("doc")
+        .current_dir(core)
+        .assert()
+        .success();
+}