Add functions to extract rows, colums and blocks

spec/board_spec.cr

@@ -3,14 +3,43 @@ require "./spec_helper"
 describe Sudoku::Board do
 
   it "initialized grid with nil values" do
-    board = Sudoku::Board.new(8, 8)
+    board = Sudoku::Board.new(9, 3)
     board.get(0, 0).should eq nil
   end
 
+  it "raises exception if board size is not divisible by block size" do
+    expect_raises(Sudoku::BoardException) do
+      Sudoku::Board.new(9, 4)
+    end
+  end
+
   it "puts numbers correctly" do
-    board = Sudoku::Board.new(8, 8)
+    board = Sudoku::Board.new(9, 3)
     board.put(1, 0, 0)
     board.get(0, 0).should eq 1
   end
 
+  it "extracts rows correctly" do
+    row = 1
+    board = Sudoku::Board.new(4, 2)
+    (0..3).each { |i| board.put(i, i, row) }
+    board.extract_row(row).should eq [0, 1, 2, 3]
+  end
+
+  it "extracts columns correctly" do
+    column = 2
+    board = Sudoku::Board.new(4, 2)
+    (0..3).each { |i| board.put(i, column, i) }
+    board.extract_column(column).should eq [0, 1, 2, 3]
+  end
+
+  it "extracts blocks correctly" do
+    board = Sudoku::Board.new(4, 2)
+    board.put(42, 2, 0)
+    board.put(43, 3, 0)
+    board.put(44, 2, 1)
+    board.put(45, 3, 1)
+    board.extract_block(3, 1).should eq [[42, 43], [44, 45]]
+  end
+
 end