diff --git a/tests_ci/dummy_image.py b/tests_ci/dummy_image.py
new file mode 100755
index 0000000..cfc71f2
--- /dev/null
+++ b/tests_ci/dummy_image.py
@@ -0,0 +1,247 @@
+#!/usr/bin/env python3
+
+import argparse
+from binascii import crc32
+import contextlib
+import gzip
+import os.path
+import sys
+import urllib.request
+import zipfile
+
+import tomlkit
+
+sys.path.append(os.path.join(sys.path[0], ".."))
+from avbroot import ota, util
+from avbroot.main import PATH_PAYLOAD
+
+ZIP_HEADER_NO_FILENAME_SIZE = 30
+
+PARTITIONS_TO_ZERO = {"product", "system", "vendor", "system_ext", "modem"}
+
+
+class Crc32Hasher:
+    existing_crc32 = None
+
+    def get_checksum(self):
+        return self.existing_crc32
+
+    def set_checksum(self, existing_crc32):
+        self.existing_crc32 = existing_crc32
+
+    def update(self, *args, **kwargs):
+        if self.existing_crc32:
+            args = args + (self.existing_crc32,)
+
+        self.existing_crc32 = crc32(*args, **kwargs)
+
+
+@contextlib.contextmanager
+def output_open(filename, mode, compress=True):
+    if compress and not filename.endswith(".gz"):
+        filename += ".gz"
+
+    if compress:
+        with gzip.GzipFile(filename, mode, compresslevel=1, mtime=0) as f:
+            yield f
+    else:
+        with open(filename, mode) as f:
+            yield f
+
+
+def output_writer(f_in, f_out, size, db=None):
+    if not f_in:
+        util.zero_n(f_out, size)
+    else:
+        crc_hash = None
+        mapping = None
+
+        if db is not None and size != 0:
+            mapping = True
+
+        if mapping:
+            crc_hash = Crc32Hasher()
+
+            # Combine sections if adjacent
+            if db and db[-1]["range"][1] == f_out.tell() - 1:
+                entry = db.pop()
+                crc_hash.set_checksum(entry["checksum"])
+                section_start = entry["range"][0]
+            else:
+                section_start = f_out.tell()
+
+            section_end = f_out.tell() + (size - 1)
+
+        util.copyfileobj_n(f_in, f_out, size, hasher=crc_hash)
+
+        if mapping:
+            db.append(
+                {
+                    "range": [section_start, section_end],
+                    "checksum": crc_hash.get_checksum(),
+                }
+            )
+
+
+def download_file(f_out, url, section):
+    crc_hash = Crc32Hasher()
+
+    req = urllib.request.Request(url)
+    req.add_header("Range", f"bytes={section['range'][0]}-{section['range'][1]}")
+    with urllib.request.urlopen(req) as data:
+        util.copyfileobj_n(
+            data, f_out, section["range"][1] - section["range"][0] + 1, hasher=crc_hash
+        )
+
+    if crc_hash.get_checksum() != int(section["checksum"], 16):
+        raise Exception(f"ERROR: Checksum of range {section['range']} doesn't match")
+
+
+def download_dummy_image(args):
+    with open(args.db, "r") as f:
+        database = f.read()
+
+    database = tomlkit.parse(database)
+
+    device_entry = database["device"].get(args.device_name)
+    if not device_entry:
+        raise Exception(f"ERROR: {args.device_name} cannot be found in the database")
+
+    # Assume we always download the beginning and end (which makes sense for a ZIP file)
+    previous_offset = 0
+    with output_open(args.output, "wb", args.compress) as f_out:
+        for section in device_entry["sections"]:
+            util.zero_n(f_out, section["range"][0] - previous_offset)
+            download_file(f_out, device_entry["url"], section)
+            previous_offset = section["range"][1] + 1
+
+
+def print_entry(db, original_filename):
+    new_map = tomlkit.array()
+    new_map.append(tomlkit.nl())
+
+    for section in db:
+        entry = tomlkit.inline_table()
+
+        for key, value in section.items():
+            entry[key] = f"{value:x}" if key == "checksum" else value
+
+        new_map.append(entry)
+
+    print("*** Add this entry to the database ***")
+    print(
+        tomlkit.dumps(
+            {
+                "device": {
+                    "new_device_name": {
+                        "filename": os.path.basename(original_filename),
+                        "url": "",
+                        "sections": new_map,
+                    }
+                }
+            }
+        )
+    )
+    print("*** End ***")
+
+
+def convert_image(args):
+    with zipfile.ZipFile(args.input, "r") as z:
+        info = z.getinfo(PATH_PAYLOAD)
+
+        with z.open(info, "r") as f:
+            _, manifest, blob_offset = ota.parse_payload(f)
+
+    file_offset = info.header_offset + ZIP_HEADER_NO_FILENAME_SIZE + len(info.filename)
+
+    partition_operations = {}
+
+    for p in manifest.partitions:
+        if p.partition_name in PARTITIONS_TO_ZERO:
+            old_data_offset = 0
+
+            # Ensure all operations are in order
+            for op in p.operations:
+                if old_data_offset > op.data_offset:
+                    raise Exception("Operations are expected to be ordered")
+                old_data_offset = op.data_offset
+
+            partition_operations[p.partition_name] = p.operations
+
+    db = []
+
+    with open(args.input, "rb") as f_in, output_open(
+        args.output, "wb", args.compress
+    ) as f_out:
+        # Copy zip data until payload.bin + payload.bin header
+        output_writer(f_in, f_out, file_offset + blob_offset, db)
+
+        # Sort partitions based on data_offset of first operation and iterate
+        for _, p_operations in sorted(
+            partition_operations.items(), key=lambda x: x[1][0].data_offset
+        ):
+            # Copy all data until first partition offset
+            output_writer(
+                f_in,
+                f_out,
+                p_operations[0].data_offset - (f_in.tell() - file_offset - blob_offset),
+                db,
+            )
+
+            for op in p_operations:
+                if f_out.tell() != (file_offset + blob_offset + op.data_offset):
+                    raise Exception("f_out should be equal to the offset")
+                output_writer(None, f_out, op.data_length, db)
+            f_in.seek(f_out.tell())
+
+        # Copy remaining data
+        f_in.seek(0, 2)
+        remaining_size = f_in.tell() - f_out.tell()
+        f_in.seek(f_out.tell())
+        output_writer(f_in, f_out, remaining_size, db)
+
+    print_entry(db, args.input)
+
+
+def parse_args(args=None):
+    parser = argparse.ArgumentParser()
+    subparsers = parser.add_subparsers(
+        dest="subcommand", required=True, help="Subcommands"
+    )
+
+    base = argparse.ArgumentParser(add_help=False)
+    base.add_argument(
+        "--compress",
+        action=argparse.BooleanOptionalAction,
+        default=True,
+        help="Compress output file",
+    )
+    base.add_argument("--output", required=True, help="Path to new OTA zip")
+
+    convert = subparsers.add_parser(
+        "convert", help="Convert full OTA zip to dummy zip", parents=[base]
+    )
+    convert.add_argument("--input", required=True, help="Path to original OTA zip")
+
+    download = subparsers.add_parser(
+        "download", help="Assemble dummy zip while downloading", parents=[base]
+    )
+    download.add_argument("--db", required=True, help="Path to database file")
+    download.add_argument("device_name", help="Name of device (as in database)")
+
+    return parser.parse_args(args=args)
+
+
+def main(args=None):
+    args = parse_args(args=args)
+
+    if args.subcommand == "convert":
+        convert_image(args)
+    elif args.subcommand == "download":
+        download_dummy_image(args)
+    else:
+        raise NotImplementedError()
+
+
+if __name__ == "__main__":
+    main()
diff --git a/tests_ci/test_db.toml b/tests_ci/test_db.toml
new file mode 100644
index 0000000..57a949a
--- /dev/null
+++ b/tests_ci/test_db.toml
@@ -0,0 +1,65 @@
+[magisk]
+filename = "magisk.apk"
+url = "https://github.com/topjohnwu/Magisk/releases/download/v25.2/Magisk-v25.2.apk"
+sha256 = "0bdc32918b6ea502dca769b1c7089200da51ea1def170824c2812925b426d509"
+
+[device.bluejay]
+filename = "bluejay-ota-tq1a.230205.002-1ec64b58.zip"
+url = "https://dl.google.com/dl/android/aosp/bluejay-ota-tq1a.230205.002-1ec64b58.zip"
+sections = [
+    {range = [0, 25781534], checksum = "2db28a01"},
+    {range = [50595563, 50613918], checksum = "6f0635b4"},
+    {range = [1870236118, 1871590329], checksum = "272a03c1"},
+    {range = [2051986898, 2081231853], checksum = "39940962"}
+]
+
+[device.bluejay.hashes]
+"boot.img" = "8131084ad95d8ffcb917bc239ffdeef6"
+"vbmeta.img" = "38bc2245f6d41877ebf92d6612d3ca04"
+"vendor_boot.img" = "4611f85f4eae65e0eca09605068d14c8"
+
+[device.bramble]
+filename = "bramble-ota-tq1a.230205.002-49f2dc71.zip"
+url = "https://dl.google.com/dl/android/aosp/bramble-ota-tq1a.230205.002-49f2dc71.zip"
+sections = [
+    {range = [0, 12759576], checksum = "b0a1b579"},
+    {range = [1155394531, 1155409742], checksum = "b018de12"},
+    {range = [1636569527, 1637452126], checksum = "b8747c8"},
+    {range = [1870498525, 1896655733], checksum = "f3d4f27b"}
+]
+
+[device.bramble.hashes]
+"boot.img" = "098500dfba880f9a61a379d342a84cc9"
+"vbmeta.img" = "17230bbb41023bd3b03aaf94203e9330"
+"vendor_boot.img" = "34e3559f2460d8ef52ccb5352e09dfec"
+
+[device.cheetah]
+filename = "cheetah-ota-tq1a.230205.002-ad27a6d7.zip"
+url = "https://dl.google.com/dl/android/aosp/cheetah-ota-tq1a.230205.002-ad27a6d7.zip"
+sections = [
+    {range = [0, 23399500], checksum = "34f19830"},
+    {range = [125881702, 125898553], checksum = "9f68fc6d"},
+    {range = [1518207067, 1518293650], checksum = "a003f2d1"},
+    {range = [1883282667, 1883297278], checksum = "9537e70d"},
+    {range = [2010705366, 2012070705], checksum = "94fdddd2"},
+    {range = [2278970391, 2307353441], checksum = "6ba7d418"}
+]
+
+[device.cheetah.hashes]
+"init_boot.img" = "7c200e0dfd1af446d68a3f009cc86f8b"
+"vbmeta.img" = "b12f7e00cc7b9152f7aaa00ab2c4bae0"
+"vendor_boot.img" = "e39682b1656b8c59ac2717f330a08bd9"
+
+[device.sunfish]
+filename = "sunfish-ota-tq1a.230205.002-536bce5f.zip"
+url = "https://dl.google.com/dl/android/aosp/sunfish-ota-tq1a.230205.002-536bce5f.zip"
+sections = [
+    {range = [0, 34269195], checksum = "93177bf6"},
+    {range = [1146499715, 1146513902], checksum = "83903c62"},
+    {range = [1610565619, 1611042042], checksum = "114b64ce"},
+    {range = [1807072291, 1809631036], checksum = "4d33dae2"}
+]
+
+[device.sunfish.hashes]
+"boot.img" = "ddd9bcf0bdc4c727f33110f90103158a"
+"vbmeta.img" = "7388afabde4bb490ddef491dd2a8fe27"