Add fallthrough statement tests

This CL adds tests for the fallthrough statement.

Bug: tint:11
Change-Id: I1bc8677e00aa9eb446a096bd2600104550480d77
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/16500
Reviewed-by: Sarah Mashayekhi <sarahmashay@google.com>

src/CMakeLists.txt

@@ -208,6 +208,7 @@ set(TINT_TEST_SRCS
   ast/decorated_variable_test.cc
   ast/else_statement_test.cc
   ast/entry_point_test.cc
+  ast/fallthrough_statement_test.cc
   ast/import_test.cc
   ast/int_literal_test.cc
   ast/location_decoration_test.cc

src/ast/fallthrough_statement.cc

@@ -30,7 +30,7 @@ bool FallthroughStatement::IsValid() const {
 
 void FallthroughStatement::to_str(std::ostream& out, size_t indent) const {
   make_indent(out, indent);
-  out << "Fallthrough" << std::endl;
+  out << "Fallthrough{}" << std::endl;
 }
 
 }  // namespace ast

src/ast/fallthrough_statement_test.cc

@@ -0,0 +1,56 @@
+// Copyright 2020 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/ast/fallthrough_statement.h"
+
+#include "gtest/gtest.h"
+
+namespace tint {
+namespace ast {
+
+using FallthroughStatementTest = testing::Test;
+
+TEST_F(FallthroughStatementTest, Creation) {
+  FallthroughStatement stmt;
+  EXPECT_EQ(stmt.line(), 0);
+  EXPECT_EQ(stmt.column(), 0);
+}
+
+TEST_F(FallthroughStatementTest, Creation_WithSource) {
+  FallthroughStatement stmt(Source{20, 2});
+  auto src = stmt.source();
+  EXPECT_EQ(src.line, 20);
+  EXPECT_EQ(src.column, 2);
+}
+
+TEST_F(FallthroughStatementTest, IsFallthrough) {
+  FallthroughStatement stmt;
+  EXPECT_TRUE(stmt.IsFallthrough());
+}
+
+TEST_F(FallthroughStatementTest, IsValid) {
+  FallthroughStatement stmt;
+  EXPECT_TRUE(stmt.IsValid());
+}
+
+TEST_F(FallthroughStatementTest, ToStr) {
+  FallthroughStatement stmt;
+  std::ostringstream out;
+  stmt.to_str(out, 2);
+  EXPECT_EQ(out.str(), R"(  Fallthrough{}
+)");
+}
+
+}  // namespace ast
+}  // namespace tint