diff --git a/clang-tools-extra/clangd/unittests/XRefsTests.cpp b/clang-tools-extra/clangd/unittests/XRefsTests.cpp
--- a/clang-tools-extra/clangd/unittests/XRefsTests.cpp
+++ b/clang-tools-extra/clangd/unittests/XRefsTests.cpp
@@ -253,7 +253,7 @@
       )cpp",
 
       R"cpp(// Function definition via pointer
-        int [[foo]](int) {}
+        void [[foo]](int) {}
         int main() {
           auto *X = &^foo;
         }
@@ -270,7 +270,7 @@
         struct Foo { int [[x]]; };
         int main() {
           Foo bar;
-          bar.^x;
+          (void)bar.^x;
         }
       )cpp",
 
@@ -322,7 +322,7 @@
 
       R"cpp(// Namespace
         namespace $decl[[ns]] {
-        struct Foo { static void bar(); }
+        struct Foo { static void bar(); };
         } // namespace ns
         int main() { ^ns::Foo::bar(); }
       )cpp",
@@ -352,7 +352,7 @@
 
       R"cpp(// Symbol concatenated inside macro (not supported)
        int *pi;
-       #define POINTER(X) p # X;
+       #define POINTER(X) p ## X;
        int i = *POINTER(^i);
       )cpp",
 
@@ -433,10 +433,10 @@
       )cpp",
 
       R"cpp(// No implicit constructors
-        class X {
+        struct X {
           X(X&& x) = default;
         };
-        X [[makeX]]() {}
+        X $decl[[makeX]]();
         void foo() {
           auto x = m^akeX();
         }
@@ -444,7 +444,7 @@
 
       R"cpp(
         struct X {
-          X& [[operator]]++() {}
+          X& [[operator]]++() { return *this; }
         };
         void foo(X& x) {
           +^+x;
@@ -529,7 +529,20 @@
     // parsing.
     TU.ExtraArgs.push_back("-fno-delayed-template-parsing");
 
+    // Disable warnings which some testcases intentionally trigger,
+    // so that we can assert the testcases have no diagnostics and
+    // catch mistakes.
+    TU.ExtraArgs.push_back("-Wno-gnu-designator");
+    TU.ExtraArgs.push_back("-Wno-macro-redefined");
+
     auto AST = TU.build();
+    // We don't expect there to be diagnostics, but if there are,
+    // it facilitates debugging to print them.
+    for (auto &Diag : AST.getDiagnostics()) {
+      llvm::errs() << Diag << "\n";
+    }
+    ASSERT_TRUE(AST.getDiagnostics().empty()) << Test;
+
     auto Results = locateSymbolAt(AST, T.point());
 
     if (!WantDecl) {