Add DataTable::isNull() (#51)

Add function `DataTable::isNull()` to address #50.
Add related test of functionality.

Author: ddbaptiste

include/DataTable.hpp

@@ -212,6 +212,8 @@ namespace Data {
         virtual DataTableShape getShape() const = 0;
 
         virtual bool empty() const = 0;
+
+        virtual bool isNull() const = 0;
     };
 
     using IDataTablePtr = std::shared_ptr<Data::IDataTable>;
@@ -568,6 +570,10 @@ namespace Data {
         /// @brief Test if the table is empty
         /// @return true if no rows, false if contains data
         bool empty() const override { return (this->nrows() == 0); }
+
+        /// @brief Test if the table contains no data at all
+        /// @return true if `this->data` is empty, false otherwise
+        bool isNull() const override { return this->data.empty(); }
     };
 } // namespace Data
 

test/DataTableTest.cpp

@@ -780,6 +780,11 @@ TEST_F(DataTableTest, TableEmptyAfterJoin) {
     EXPECT_TRUE(resultTable->empty());
 }
 
+TEST_F(DataTableTest, TableNull) {
+    Data::DataTable dt;
+    EXPECT_TRUE(dt.isNull());
+}
+
 TEST_F(DataTableTest, innerJoin) {
     std::vector<std::string> headerOrder1 = {"id", "test1", "test2", "test3"};
     std::map<std::string, std::vector<std::string>> d1;