Improve coverage again

Author: jiahao

test/combinations.jl

@@ -19,4 +19,5 @@ import Combinatorics: combinations
 @test_throws DomainError collect(CoolLexCombinations(-1, 1))
 @test_throws DomainError collect(CoolLexCombinations(5, 0))
 @test collect(CoolLexCombinations(4,2)) == Vector[[1,2], [2,3], [1,3], [2,4], [3,4], [1,4]]
+@test isa(start(CoolLexCombinations(1000, 20)), Combinatorics.CoolLexIterState{BigInt})
 

test/numbers.jl

@@ -4,6 +4,7 @@ using Base.Test
 # catalan
 @test catalannum(5) == 42
 @test catalannum(30) == parse(BigInt,"3814986502092304")
+@test_throws DomainError catalannum(-1)
 
 # fibonacci
 @test fibonaccinum(5) == 5