diff --git a/src/machine.jl b/src/machine.jl
index 7784774c..4d8499f9 100644
--- a/src/machine.jl
+++ b/src/machine.jl
@@ -212,7 +212,7 @@ function throw_input_error(
         string(index),
         ".\nLast ",
         string(length(slice)),
-        " bytes were:\n\n"
+        " byte(s) were:\n\n"
     )
     write(buf, bytes, "\n\n")
 
diff --git a/test/byteset.jl b/test/byteset.jl
new file mode 100644
index 00000000..bdf265fc
--- /dev/null
+++ b/test/byteset.jl
@@ -0,0 +1,77 @@
+module TestByteSet
+
+using Automa: Automa, ByteSet
+using Test
+
+
+function test_membership(members)
+    bs = ByteSet(members)
+    refset = Set{UInt8}([UInt8(i) for i in  members])
+    @test refset == Set{UInt8}(collect(bs))
+    @test all(i -> in(i, bs), refset)
+end
+
+function test_inversion(bs)
+    inv = ~bs
+    all = true
+    for i in 0x00:0xff
+        all &= (in(i, bs) ⊻ in(i, inv))
+    end
+    @test all
+end
+
+@testset "Instantiation" begin
+    @test isempty(ByteSet())
+    @test iszero(length(ByteSet()))
+
+    for set in ["hello", "kdjy82zxxcbnpw", [0x00, 0x1a, 0xff, 0xf8, 0xd2]]
+        test_membership(set)
+    end
+end
+
+@testset "Min/max" begin
+    @test_throws ArgumentError maximum(ByteSet())
+    @test_throws ArgumentError minimum(ByteSet())
+    @test minimum(ByteSet("xylophone")) == UInt8('e')
+    @test maximum(ByteSet([0xa1, 0x0f, 0x4e, 0xf1, 0x40, 0x39])) == 0xf1
+end
+
+@testset "Contiguity" begin
+    @test Automa.is_contiguous(ByteSet(0x03:0x41))
+    @test Automa.is_contiguous(ByteSet())
+    @test Automa.is_contiguous(ByteSet(0x51))
+    @test Automa.is_contiguous(ByteSet(0xc1:0xd2))
+    @test Automa.is_contiguous(ByteSet(0x00:0xff))
+
+    @test !Automa.is_contiguous(ByteSet([0x12:0x3a; 0x3c:0x4a]))
+    @test !Automa.is_contiguous(ByteSet([0x01, 0x02, 0x04, 0x05]))
+end
+
+@testset "Inversion" begin
+    test_inversion(ByteSet())
+    test_inversion(ByteSet(0x00:0xff))
+    test_inversion(ByteSet([0x04, 0x06, 0x91, 0x92]))
+    test_inversion(ByteSet(0x54:0x71))
+    test_inversion(ByteSet(0x12:0x11))
+    test_inversion(ByteSet("abracadabra"))
+end
+
+@testset "Set operations" begin
+    sets = map(ByteSet, [
+        [],
+        [0x00:0xff;],
+        [0x00:0x02; 0x04; 0x19],
+        [0x01; 0x03; 0x09; 0xa1; 0xa1],
+        [0x41:0x8f; 0xd1:0xe1; 0xa0:0xf0],
+        [0x81:0x89; 0xd0:0xd0]
+    ])
+    ssets = map(Set, sets)
+    for (s1, ss1) in zip(sets, ssets), (s2, ss2) in zip(sets, ssets)
+        for f in [union, intersect, symdiff, setdiff]
+            @test Set(f(s1, s2)) == f(ss1, ss2)
+        end
+        @test isdisjoint(s1, s2) == isdisjoint(ss1, ss2)
+    end
+end
+
+end # module
diff --git a/test/input_error.jl b/test/input_error.jl
new file mode 100644
index 00000000..0cb1e2cd
--- /dev/null
+++ b/test/input_error.jl
@@ -0,0 +1,15 @@
+module TestInputError
+
+using Automa
+using Test
+
+@testset "Input error" begin
+    machine = compile(re"xyz")
+    @eval function test_input_error(data)
+        $(generate_code(machine))
+    end
+
+    @test_throws Exception test_input_error("a")
+end
+
+end # module
diff --git a/test/runtests.jl b/test/runtests.jl
index 50ddacfd..56ccebef 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -32,10 +32,7 @@ using Test
 end
 
 @testset "ByteSet" begin
-    x = Automa.ByteSet()
-    @test isempty(x)
-    @test_throws ArgumentError minimum(x)
-    @test_throws ArgumentError maximum(x)
+    include("byteset.jl")
 end
 
 @testset "RegExp" begin
@@ -124,6 +121,7 @@ include("test16.jl")
 include("test17.jl")
 include("test18.jl")
 include("test19.jl")
+include("input_error.jl")
 include("simd.jl")
 include("unicode.jl")
 include("validator.jl")
diff --git a/test/test11.jl b/test/test11.jl
index cef20e85..907b2949 100644
--- a/test/test11.jl
+++ b/test/test11.jl
@@ -4,6 +4,8 @@ using Automa
 using Test
 
 @testset "Test11" begin
+    @test_throws Exception precond!(re"A", :foo; when=:never)
+
     a = re"[a-z]+"
     precond!(a, :le)
     a = rep1(a)