bios: Implement BIOSStringAttribute

Implement BIOSStringAttribute, most of the code is copied from
bios/bios_parser.cpp.

Implement SetAttrValueOnDbus and constructEntry for string attribute

Signed-off-by: John Wang <wangzqbj@inspur.com>
Change-Id: Ic7c6b35d32738d698d7649f97cb7843606b8a2ba
diff --git a/test/mocked_bios.hpp b/test/mocked_bios.hpp
new file mode 100644
index 0000000..eb95c33
--- /dev/null
+++ b/test/mocked_bios.hpp
@@ -0,0 +1,57 @@
+#include "libpldmresponder/bios_table.hpp"
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+using testing::ElementsAreArray;
+using namespace pldm::responder::bios;
+
+class MockBIOSStringTable : public BIOSStringTable
+{
+  public:
+    MockBIOSStringTable() : BIOSStringTable({})
+    {
+    }
+
+    MOCK_METHOD(uint16_t, findHandle, (const std::string&), (const override));
+};
+
+void checkHeader(const Table& attrEntry, const Table& attrValueEntry)
+{
+    auto attrHeader = table::attribute::decodeHeader(
+        reinterpret_cast<const pldm_bios_attr_table_entry*>(attrEntry.data()));
+    auto attrValueHeader = table::attribute_value::decodeHeader(
+        reinterpret_cast<const pldm_bios_attr_val_table_entry*>(
+            attrValueEntry.data()));
+
+    EXPECT_EQ(attrHeader.attrHandle, attrValueHeader.attrHandle);
+}
+
+void checkEntry(Table& entry, Table& expectedEntry)
+{
+    /** backup the attr handle */
+    auto attr0 = entry[0], eAttr0 = expectedEntry[0];
+    auto attr1 = entry[1], eAttr1 = expectedEntry[1];
+
+    /** attr handle is computed by libpldm, set it to 0 to test */
+    entry[0] = 0, expectedEntry[0] = 0;
+    entry[1] = 0, expectedEntry[1] = 0;
+
+    EXPECT_THAT(entry, ElementsAreArray(expectedEntry));
+
+    /** restore the attr handle */
+    entry[0] = attr0, expectedEntry[0] = eAttr0;
+    entry[1] = attr1, expectedEntry[1] = eAttr1;
+}
+
+void checkConstructEntry(BIOSAttribute& attribute, BIOSStringTable& stringTable,
+                         Table& expectedAttrEntry,
+                         Table& expectedAttrValueEntry)
+{
+    Table attrEntry, attrValueEntry;
+    attribute.constructEntry(stringTable, attrEntry, attrValueEntry);
+
+    checkHeader(attrEntry, attrValueEntry);
+    checkEntry(attrEntry, expectedAttrEntry);
+    checkEntry(attrValueEntry, expectedAttrValueEntry);
+}
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