Add a test for BigInteger::operator<<

Author: abolz

test/unittest/bigintegertest.cpp

@@ -120,6 +120,11 @@ TEST(BigInteger, LeftShift) {
     EXPECT_TRUE(BIGINTEGER_LITERAL("4537899042132549697536") == a);
     a <<= 99;
     EXPECT_TRUE(BIGINTEGER_LITERAL("2876235222267216943024851750785644982682875244576768") == a);
+
+    a = 1;
+    a <<= 64; // a.count_ != 1
+    a <<= 256; // interShift == 0
+    EXPECT_TRUE(BIGINTEGER_LITERAL("2135987035920910082395021706169552114602704522356652769947041607822219725780640550022962086936576") == a);
 }
 
 TEST(BigInteger, Compare) {