Remove unused variable (and add test for it)

Author: tompng

lib/bigdecimal/math.rb

@@ -778,7 +778,6 @@ def lgamma(x, prec)
       # if x is close to 1 or 2, increase precision to reduce loss of significance
       diff1_exponent = (x - 1).exponent
       diff2_exponent = (x - 2).exponent
-      extra_prec = [-diff1_exponent, -diff2_exponent, 0].max
       extremely_near_one = diff1_exponent < -prec2
       extremely_near_two = diff2_exponent < -prec2
 

test/bigdecimal/test_bigmath.rb

@@ -14,6 +14,13 @@ class TestBigMath < Test::Unit::TestCase
   MINF = BigDecimal("-Infinity")
   NAN = BigDecimal("NaN")
 
+  def test_no_warning
+    assert_separately([], "#{<<~"begin;"}\n#{<<~'end;'}")
+    begin;
+      require 'bigdecimal/math'
+    end;
+  end
+
   def test_pi
     assert_equal(
       BigDecimal("3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117068"),