diff --git a/src/github.com/matrix-org/dendrite/roomserver/input/state_test.go b/src/github.com/matrix-org/dendrite/roomserver/input/state_test.go
new file mode 100644
index 000000000..e5707ff1a
--- /dev/null
+++ b/src/github.com/matrix-org/dendrite/roomserver/input/state_test.go
@@ -0,0 +1,67 @@
+package input
+
+import (
+	"github.com/matrix-org/dendrite/roomserver/types"
+	"testing"
+)
+
+type sortBytes []byte
+
+func (s sortBytes) Len() int           { return len(s) }
+func (s sortBytes) Less(i, j int) bool { return s[i] < s[j] }
+func (s sortBytes) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+
+func TestUnique(t *testing.T) {
+	testCases := []struct {
+		Input string
+		Want  string
+	}{
+		{"", ""},
+		{"abc", "abc"},
+		{"aaabbbccc", "abc"},
+	}
+
+	for _, test := range testCases {
+		input := []byte(test.Input)
+		want := string(test.Want)
+		got := string(input[:unique(sortBytes(input))])
+		if got != want {
+			t.Fatal("Wanted ", want, " got ", got)
+		}
+	}
+}
+
+func TestFindDuplicateStateKeys(t *testing.T) {
+	testCases := []struct {
+		Input []types.StateEntry
+		Want  []types.StateEntry
+	}{{
+		Input: []types.StateEntry{
+			{types.StateKeyTuple{1, 1}, 1},
+			{types.StateKeyTuple{1, 1}, 2},
+			{types.StateKeyTuple{2, 2}, 3},
+		},
+		Want: []types.StateEntry{
+			{types.StateKeyTuple{1, 1}, 1},
+			{types.StateKeyTuple{1, 1}, 2},
+		},
+	}, {
+		Input: []types.StateEntry{
+			{types.StateKeyTuple{1, 1}, 1},
+			{types.StateKeyTuple{1, 2}, 2},
+		},
+		Want: nil,
+	}}
+
+	for _, test := range testCases {
+		got := findDuplicateStateKeys(test.Input)
+		if len(got) != len(test.Want) {
+			t.Fatalf("Wanted %v, got %v", test.Want, got)
+		}
+		for i := range got {
+			if got[i] != test.Want[i] {
+				t.Fatalf("Wanted %v, got %v", test.Want, got)
+			}
+		}
+	}
+}