Improve test coverage

Author: chfw

pyexcel_io/book.py

@@ -164,7 +164,10 @@ def write(self, incoming_dict):
                 sheet_writer.close()
 
     def create_sheet(self, sheet_name):
-        pass
+        """
+        implement this method for easy extension
+        """
+        raise NotImplementedError("Please implement create_sheet()")
 
 
 def _convert_content_to_stream(file_content, file_type):

pyexcel_io/sheet.py

@@ -137,7 +137,7 @@ def write_row(self, array):
         """
         write a row into the file
         """
-        raise NotImplementedError("Please implement write_row")
+        raise NotImplementedError("Please implement write_row()")
 
     def write_array(self, table):
         """

tests/test_base.py

@@ -1,11 +1,17 @@
 from pyexcel_io.sheet import (
-    SheetReader,
-    SheetWriter, NamedContent
+    SheetReader, SheetWriter, NamedContent
 )
+from pyexcel_io.book import BookWriter
 from pyexcel_io.utils import is_empty_array
 from nose.tools import raises
 
 
+@raises(NotImplementedError)
+def test_book_writer():
+    book = BookWriter()
+    book.create_sheet("test")
+
+
 def test_is_empty_array():
     a = ["", "", "", ""]
     assert is_empty_array(a) is True
@@ -47,6 +53,16 @@ def test_abstractness(self):
         reader = SheetReader("test")
         reader.cell_value(1, 2)
 
+    @raises(NotImplementedError)
+    def test_number_of_columns(self):
+        reader = SheetReader("test")
+        reader.number_of_columns()
+
+    @raises(NotImplementedError)
+    def test_number_of_rows(self):
+        reader = SheetReader("test")
+        reader.number_of_rows()
+
     def test_to_array(self):
         name = "test"