How can I manually / programmatically create a DataRow?

You should note that if the Unit Test needed to enforce type constraints on the DataColumnCollection (Columns) for the DataTable - you can use the overloaded constructor of the DataColumn class to include the expected Type.

        var dt = new DataTable();
        
        var dc = new DataColumn("Age", typeof(int));
        dt.Columns.Add(dc);
        var dr = dt.NewRow();

        dr["Age"] = "test"; // throws an ArgumentException
        //Input string was not in a correct format. Couldn't store<test> in Age Column.  Expected type is Int32.

        //should it succeed
        dt.Rows.Add(dr);

A DataRow can be created by creating a new DataTable instance, adding columns to the DataTable corresponding to the "keys" that the DataRow needs to have, and then calling NewRow() on the DataTable. For example:

DataTable usersTable = new DataTable();

usersTable.Columns.Add("FirstName");
usersTable.Columns.Add("LastName");
usersTable.Columns.Add("Email");

DataRow userRow = usersTable.NewRow();

userRow["FirstName"] = "Elmer";
userRow["LastName"] = "Example";
userRow["Email"] = "[email protected]";
usersTable.Rows.Add(userRow);