Add `struct string` for strings parsed from FDT

Just a small wrapper around a char array to make things simpler.

Bug: 117551352
Change-Id: I0880ebbb81258830290ce49bf3772280551d3483
diff --git a/src/string_test.cc b/src/string_test.cc
new file mode 100644
index 0000000..f814636
--- /dev/null
+++ b/src/string_test.cc
@@ -0,0 +1,66 @@
+/*
+ * Copyright 2019 The Hafnium 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
+ *
+ *     https://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 <gmock/gmock.h>
+
+extern "C" {
+#include "hf/string.h"
+}
+
+namespace
+{
+TEST(string, valid)
+{
+	struct string str;
+	constexpr const char data[] = "test";
+
+	string_init_empty(&str);
+	ASSERT_TRUE(string_is_empty(&str));
+	ASSERT_STREQ(string_data(&str), "");
+
+	ASSERT_EQ(string_init(&str, data, sizeof(data)), STRING_SUCCESS);
+	ASSERT_FALSE(string_is_empty(&str));
+	ASSERT_STRNE(string_data(&str), "");
+	ASSERT_STREQ(string_data(&str), "test");
+}
+
+TEST(string, data_zero_size)
+{
+	struct string str;
+	constexpr const char data[] = "test";
+
+	ASSERT_EQ(string_init(&str, data, 0), STRING_ERROR_INVALID_INPUT);
+}
+
+TEST(string, data_no_null_terminator)
+{
+	struct string str;
+	constexpr const char data[] = {'t', 'e', 's', 't'};
+
+	ASSERT_EQ(string_init(&str, data, sizeof(data)),
+		  STRING_ERROR_INVALID_INPUT);
+}
+
+TEST(string, data_two_null_terminators)
+{
+	struct string str;
+	constexpr const char data[] = {'\0', 't', 'e', 's', 't', '\0'};
+
+	ASSERT_EQ(string_init(&str, data, sizeof(data)),
+		  STRING_ERROR_INVALID_INPUT);
+}
+
+} /* namespace */