[Test] add test_array2hexstring

tests/test_npy2hls.py

+from finn.core.datatype import DataType
+from finn.core.utils import array2hexstring
+
+
+def test_array2hexstring():
+    assert array2hexstring([1, 1, 1, 0], DataType.BINARY, 4) == "e"
+    assert array2hexstring([1, 1, 1, 0], DataType.BINARY, 8) == "0e"
+    assert array2hexstring([1, 1, 1, -1], DataType.BIPOLAR, 8) == "0e"
+    assert array2hexstring([3, 3, 3, 3], DataType.UINT2, 8) == "ff"
+    assert array2hexstring([1, 3, 3, 1], DataType.UINT2, 8) == "7d"
+    assert array2hexstring([1, -1, 1, -1], DataType.INT2, 8) == "77"
+    assert array2hexstring([1, 1, 1, -1], DataType.INT4, 16) == "111f"
+    assert array2hexstring([-1], DataType.FLOAT32, 32) == "bf800000"
+    assert array2hexstring([17.125], DataType.FLOAT32, 32) == "41890000"