writer/spirv: Inherit TestHelperBase from ast::Builder

Exposes all the AST builder helpers to the spirv writer tests

Change-Id: Ie6709cc9f941a52899285ad476e8b4fc7ee9e4d6
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/32983
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: dan sinclair <dsinclair@chromium.org>

src/writer/spirv/test_helper.h

@@ -19,6 +19,7 @@
 #include <utility>
 
 #include "gtest/gtest.h"
+#include "src/ast/builder.h"
 #include "src/ast/module.h"
 #include "src/context.h"
 #include "src/type_determiner.h"
@@ -30,28 +31,24 @@ namespace spirv {
 
 /// Helper class for testing
 template <typename BASE>
-class TestHelperBase : public BASE {
+class TestHelperBase : public ast::BuilderWithContext, public BASE {
  public:
-  TestHelperBase() : td(&ctx, &mod), b(&ctx, &mod) {}
+  TestHelperBase() : td(ctx, &mod), b(ctx, &mod) {}
   ~TestHelperBase() = default;
 
-  /// Creates a new `ast::Node` owned by the Context. When the Context is
-  /// destructed, the `ast::Node` will also be destructed.
-  /// @param args the arguments to pass to the type constructor
-  /// @returns the node pointer
-  template <typename T, typename... ARGS>
-  T* create(ARGS&&... args) {
-    return ctx.create<T>(std::forward<ARGS>(args)...);
-  }
-
-  /// The context
-  Context ctx;
   /// The module
   ast::Module mod;
   /// The type determiner
   TypeDeterminer td;
   /// The generator
-  Builder b;
+  spirv::Builder b;
+
+ protected:
+  /// Called whenever a new variable is built with `Var()`.
+  /// @param var the variable that was built
+  void OnVariableBuilt(ast::Variable* var) override {
+    td.RegisterVariableForTesting(var);
+  }
 };
 using TestHelper = TestHelperBase<testing::Test>;