test(xatu): cover nested let ordering

src/xatu/testdata/lint_findings.nix

@@ -1,10 +1,17 @@
 let
-  second = 2;
+  second = first;
   first = 1;
+  nested = let
+    nestedFirst = first;
+    nestedSecond = nestedFirst;
+  in {
+    result = nestedSecond;
+  };
 in {
   package = package;
   from = pkgs.from;
   url = https://example.com;
   firstField = first;
   secondField = second;
+  nestedField = nested;
 }

src/xatu/xatu_test.rs

@@ -42,17 +42,15 @@ fn xatu_rejects_invalid_source() -> googletest::Result<()> {
 }
 
 #[gtest]
-fn xatu_reports_out_of_order_let_binding() -> googletest::Result<()> {
+fn xatu_reports_out_of_order_let_bindings() -> googletest::Result<()> {
     let report = xatu::future_sight(vec![fixture_source("testdata/lint_findings.nix")?]).or_fail()?;
 
-    expect_that!(
-        report
-            .diagnostics
-            .iter()
-            .map(|diagnostic| diagnostic.finding.rule_id)
-            .collect::<Vec<_>>(),
-        contains(eq(&"let_order"))
-    );
+    let let_order_count = report
+        .diagnostics
+        .iter()
+        .filter(|diagnostic| diagnostic.finding.rule_id == "let_order")
+        .count();
+    expect_that!(let_order_count, eq(4));
     Ok(())
 }