diff --git a/klamath/test_elements.py b/klamath/test_elements.py
new file mode 100644
index 0000000..c1993c2
--- /dev/null
+++ b/klamath/test_elements.py
@@ -0,0 +1,110 @@
+import io
+import numpy
+from numpy.testing import assert_array_equal
+from klamath.elements import Boundary, Path, Text, Reference, Box, Node
+
+def test_boundary_roundtrip() -> None:
+    xy = numpy.array([[0, 0], [10, 0], [10, 10], [0, 10], [0, 0]], dtype=numpy.int32)
+    b = Boundary(layer=(4, 5), xy=xy, properties={1: b'prop1'})
+
+    stream = io.BytesIO()
+    b.write(stream)
+    stream.seek(0)
+
+    b2 = Boundary.read(stream)
+    assert b2.layer == b.layer
+    assert_array_equal(b2.xy, b.xy)
+    assert b2.properties == b.properties
+
+def test_path_roundtrip() -> None:
+    xy = numpy.array([[0, 0], [100, 0], [100, 100]], dtype=numpy.int32)
+    p = Path(layer=(10, 20), xy=xy, properties={2: b'pathprop'},
+             path_type=4, width=50, extension=(10, 20))
+
+    stream = io.BytesIO()
+    p.write(stream)
+    stream.seek(0)
+
+    p2 = Path.read(stream)
+    assert p2.layer == p.layer
+    assert_array_equal(p2.xy, p.xy)
+    assert p2.properties == p.properties
+    assert p2.path_type == p.path_type
+    assert p2.width == p.width
+    assert p2.extension == p.extension
+
+def test_text_roundtrip() -> None:
+    xy = numpy.array([[50, 50]], dtype=numpy.int32)
+    t = Text(layer=(1, 1), xy=xy, string=b"HELLO WORLD", properties={},
+             presentation=5, path_type=0, width=0, invert_y=True,
+             mag=2.5, angle_deg=45.0)
+
+    stream = io.BytesIO()
+    t.write(stream)
+    stream.seek(0)
+
+    t2 = Text.read(stream)
+    assert t2.layer == t.layer
+    assert_array_equal(t2.xy, t.xy)
+    assert t2.string == t.string
+    assert t2.presentation == t.presentation
+    assert t2.invert_y == t.invert_y
+    assert t2.mag == t.mag
+    assert t2.angle_deg == t.angle_deg
+
+def test_reference_sref_roundtrip() -> None:
+    xy = numpy.array([[100, 200]], dtype=numpy.int32)
+    r = Reference(struct_name=b"MY_CELL", xy=xy, colrow=None,
+                  properties={5: b'sref'}, invert_y=False, mag=1.0, angle_deg=90.0)
+
+    stream = io.BytesIO()
+    r.write(stream)
+    stream.seek(0)
+
+    r2 = Reference.read(stream)
+    assert r2.struct_name == r.struct_name
+    assert_array_equal(r2.xy, r.xy)
+    assert r2.colrow is None
+    assert r2.properties == r.properties
+    assert r2.angle_deg == r.angle_deg
+
+def test_reference_aref_roundtrip() -> None:
+    xy = numpy.array([[0, 0], [1000, 0], [0, 500]], dtype=numpy.int32)
+    colrow = (5, 2)
+    r = Reference(struct_name=b"ARRAY_CELL", xy=xy, colrow=colrow,
+                  properties={}, invert_y=False, mag=1.0, angle_deg=0.0)
+
+    stream = io.BytesIO()
+    r.write(stream)
+    stream.seek(0)
+
+    r2 = Reference.read(stream)
+    assert r2.struct_name == r.struct_name
+    assert_array_equal(r2.xy, r.xy)
+    assert r2.colrow is not None
+    assert list(r2.colrow) == list(colrow)
+    assert r2.properties == r.properties
+
+def test_box_roundtrip() -> None:
+    xy = numpy.array([[0, 0], [10, 0], [10, 10], [0, 10], [0, 0]], dtype=numpy.int32)
+    b = Box(layer=(30, 40), xy=xy, properties={})
+
+    stream = io.BytesIO()
+    b.write(stream)
+    stream.seek(0)
+
+    b2 = Box.read(stream)
+    assert b2.layer == b.layer
+    assert_array_equal(b2.xy, b.xy)
+
+def test_node_roundtrip() -> None:
+    xy = numpy.array([[0, 0], [10, 10]], dtype=numpy.int32)
+    n = Node(layer=(50, 60), xy=xy, properties={})
+
+    stream = io.BytesIO()
+    n.write(stream)
+    stream.seek(0)
+
+    n2 = Node.read(stream)
+    assert n2.layer == n.layer
+    assert_array_equal(n2.xy, n.xy)
diff --git a/klamath/test_library.py b/klamath/test_library.py
new file mode 100644
index 0000000..27ee41b
--- /dev/null
+++ b/klamath/test_library.py
@@ -0,0 +1,78 @@
+import io
+import numpy
+from datetime import datetime
+from klamath.library import FileHeader, write_struct, try_read_struct, scan_structs, scan_hierarchy, read_elements
+from klamath.elements import Boundary
+from klamath.records import ENDLIB
+
+def test_file_header_roundtrip() -> None:
+    h = FileHeader(name=b"MY_LIB", user_units_per_db_unit=0.001, meters_per_db_unit=1e-9,
+                   mod_time=datetime(2023, 1, 1, 0, 0, 0), acc_time=datetime(2023, 1, 1, 0, 0, 0))
+
+    stream = io.BytesIO()
+    h.write(stream)
+    stream.seek(0)
+
+    h2 = FileHeader.read(stream)
+    assert h2.name == h.name
+    assert h2.user_units_per_db_unit == h.user_units_per_db_unit
+    assert h2.meters_per_db_unit == h.meters_per_db_unit
+    assert h2.mod_time == h.mod_time
+
+def test_write_read_struct() -> None:
+    xy = numpy.array([[0, 0], [10, 0], [10, 10], [0, 10], [0, 0]], dtype=numpy.int32)
+    b = Boundary(layer=(1, 1), xy=xy, properties={})
+
+    stream = io.BytesIO()
+    # Need a header for some operations, but write_struct works standalone
+    write_struct(stream, name=b"CELL_A", elements=[b])
+    ENDLIB.write(stream, None)
+    stream.seek(0)
+
+    res = try_read_struct(stream)
+    assert res is not None
+    name, elements = res
+    assert name == b"CELL_A"
+    assert len(elements) == 1
+    assert isinstance(elements[0], Boundary)
+
+def test_scan_structs() -> None:
+    stream = io.BytesIO()
+    write_struct(stream, name=b"CELL_A", elements=[])
+    write_struct(stream, name=b"CELL_B", elements=[])
+    ENDLIB.write(stream, None)
+    stream.seek(0)
+
+    positions = scan_structs(stream)
+    assert b"CELL_A" in positions
+    assert b"CELL_B" in positions
+
+    # Verify we can seek and read
+    stream.seek(positions[b"CELL_B"])
+    elements = read_elements(stream)
+    assert len(elements) == 0
+
+def test_scan_hierarchy() -> None:
+    from klamath.elements import Reference
+
+    stream = io.BytesIO()
+    # Struct A has 2 refs to Struct B
+    ref_b1 = Reference(struct_name=b"B", xy=numpy.array([[0, 0]], dtype=numpy.int32), colrow=None, properties={},
+                       invert_y=False, mag=1.0, angle_deg=0.0)
+    ref_b2 = Reference(struct_name=b"B", xy=numpy.array([[10, 10]], dtype=numpy.int32), colrow=None, properties={},
+                       invert_y=False, mag=1.0, angle_deg=0.0)
+    write_struct(stream, name=b"A", elements=[ref_b1, ref_b2])
+
+    # Struct B has a 3x2 AREF of Struct C
+    ref_c = Reference(struct_name=b"C", xy=numpy.array([[0, 0], [10, 0], [0, 10]], dtype=numpy.int32),
+                      colrow=(3, 2), properties={}, invert_y=False, mag=1.0, angle_deg=0.0)
+    write_struct(stream, name=b"B", elements=[ref_c])
+
+    write_struct(stream, name=b"C", elements=[])
+    ENDLIB.write(stream, None)
+    stream.seek(0)
+
+    hierarchy = scan_hierarchy(stream)
+    assert hierarchy[b"A"] == {b"B": 2}
+    assert hierarchy[b"B"] == {b"C": 6}
+    assert hierarchy[b"C"] == {}
diff --git a/klamath/test_record.py b/klamath/test_record.py
new file mode 100644
index 0000000..99a5a1f
--- /dev/null
+++ b/klamath/test_record.py
@@ -0,0 +1,134 @@
+import io
+import pytest
+import struct
+from datetime import datetime
+from klamath.basic import KlamathError
+from klamath.record import (
+    write_record_header, read_record_header, expect_record,
+    BitArrayRecord, Int2Record, ASCIIRecord, DateTimeRecord, NoDataRecord
+)
+from klamath.records import ENDLIB, HEADER
+
+def test_write_read_record_header() -> None:
+    stream = io.BytesIO()
+    tag = 0x1234
+    data_size = 8
+
+    write_record_header(stream, data_size, tag)
+    stream.seek(0)
+
+    read_size, read_tag = read_record_header(stream)
+    assert read_size == data_size
+    assert read_tag == tag
+    assert stream.tell() == 4
+
+def test_write_record_header_too_big() -> None:
+    stream = io.BytesIO()
+    with pytest.raises(KlamathError, match="Record size is too big"):
+        write_record_header(stream, 0x10000, 0x1234)
+
+def test_read_record_header_errors() -> None:
+    # Too small
+    stream = io.BytesIO(struct.pack('>HH', 2, 0x1234))
+    with pytest.raises(KlamathError, match="Record size is too small"):
+        read_record_header(stream)
+
+    # Odd size
+    stream = io.BytesIO(struct.pack('>HH', 5, 0x1234))
+    with pytest.raises(KlamathError, match="Record size is odd"):
+        read_record_header(stream)
+
+def test_expect_record() -> None:
+    stream = io.BytesIO()
+    write_record_header(stream, 4, 0x1111)
+    stream.seek(0)
+
+    # Correct tag
+    size = expect_record(stream, 0x1111)
+    assert size == 4
+
+    # Incorrect tag
+    stream.seek(0)
+    with pytest.raises(KlamathError, match="Unexpected record"):
+        expect_record(stream, 0x2222)
+
+def test_bitarray_record() -> None:
+    class TestBit(BitArrayRecord):
+        tag = 0x9999
+
+    stream = io.BytesIO()
+    TestBit.write(stream, 0x8000)
+    stream.seek(0)
+
+    val = TestBit.read(stream)
+    assert val == 0x8000
+
+def test_int2_record() -> None:
+    class TestInt2(Int2Record):
+        tag = 0x8888
+
+    stream = io.BytesIO()
+    TestInt2.write(stream, [1, -2, 3])
+    stream.seek(0)
+
+    val = TestInt2.read(stream)
+    assert list(val) == [1, -2, 3]
+
+def test_ascii_record() -> None:
+    class TestASCII(ASCIIRecord):
+        tag = 0x7777
+
+    stream = io.BytesIO()
+    TestASCII.write(stream, b"HELLO")
+    stream.seek(0)
+
+    val = TestASCII.read(stream)
+    assert val == b"HELLO"
+
+def test_datetime_record() -> None:
+    class TestDT(DateTimeRecord):
+        tag = 0x6666
+
+    now = datetime(2023, 10, 27, 12, 30, 45)
+    stream = io.BytesIO()
+    TestDT.write(stream, [now, now])
+    stream.seek(0)
+
+    vals = TestDT.read(stream)
+    assert vals == [now, now]
+
+def test_nodata_record() -> None:
+    class TestNoData(NoDataRecord):
+        tag = 0x5555
+
+    stream = io.BytesIO()
+    TestNoData.write(stream, None)
+    stream.seek(0)
+
+    # Verify header: 4 bytes total (size=4, tag=0x5555), data_size=0
+    header = stream.read(4)
+    assert header == struct.pack('>HH', 4, 0x5555)
+
+    stream.seek(0)
+    assert TestNoData.read(stream) is None
+
+def test_record_skip_past() -> None:
+    stream = io.BytesIO()
+    HEADER.write(stream, 600)
+    ENDLIB.write(stream, None)
+
+    stream.seek(0)
+    # Skip past HEADER
+    found = HEADER.skip_past(stream)
+    assert found is True
+    assert stream.tell() == 6 # 4 header + 2 data
+
+    # Try to skip past something that doesn't exist before ENDLIB
+    class NONEXISTENT(NoDataRecord):
+        tag = 0xFFFF
+
+    stream.seek(0)
+    found = NONEXISTENT.skip_past(stream)
+    assert found is False
+    # Should be at the end of ENDLIB record header/tag read
+    assert stream.tell() == 10 # 6 (HEADER) + 4 (ENDLIB)