class_docstr: Tests for NgramCounter that only involve lookup, no modification.
class_docstr_tok: ["Tests","for","NgramCounter","that","only","involve","lookup",",","no","modification","."]
code: def test_bigram_counts_seen_ngrams(self):
      assert self.bigram_counter[["a"]]["b"] == 1
      assert self.bigram_counter[["b"]]["c"] == 1
  
imports: import unittest
  import pytest
  from nltk import FreqDist
  from nltk.lm import NgramCounter
  from nltk.util import everygrams
label_desc: Use image node_id 6 for calling the TestNgramCounter obj's underlying member method code with example usage: obj.test_bigram_counts_seen_ngrams() without return types