diff --git a/pyproject.toml b/pyproject.toml
index 1107b88..69dc879 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -3,7 +3,7 @@ requires = ["setuptools", "setuptools-scm", "setuptools-git-versioning"]
 build-backend = "setuptools.build_meta"
 
 [project]
-dependencies = ["typer>=0.24.1"]
+dependencies = ["polars>=1.39.3", "typer>=0.24.1"]
 dynamic = ["version"]
 name = "tsoppy"
 requires-python = ">=3.14"
@@ -12,7 +12,7 @@ requires-python = ">=3.14"
 tsoppy = "tsoppy.cli:app"
 
 [project.optional-dependencies]
-dev = ["isort==8.0.1", "ruff==0.15.6"]
+dev = ["isort==8.0.1", "pytest==9.0.2", "ruff==0.15.6"]
 lint = ["ruff==0.15.6"]
 test = ["pytest==9.0.2", "pytest-emoji==0.2.0", "pytest-md==0.2.0"]
 
diff --git a/src/tsoppy/cli.py b/src/tsoppy/cli.py
index 3c0030a..8dabc70 100644
--- a/src/tsoppy/cli.py
+++ b/src/tsoppy/cli.py
@@ -3,11 +3,27 @@
 """
 
 import importlib.metadata
+import logging
+import re
+from pathlib import Path
 from typing import Annotated
 
 import typer
 
+from tsoppy.update_small_variant_vcf_list.main import VcfList
+
+# Set up logging for the CLI. The logging level is set to INFO, and the log messages will include the timestamp, log level, and message.
+logging.basicConfig(
+    level=logging.INFO,
+    format="%(asctime)s %(levelname)s: %(message)s",
+    datefmt="%Y/%m/%d %H:%M:%S",
+)
+logger = logging.getLogger(__name__)
+
+# Create a Typer app for the CLI. The app will be used to define the commands and their arguments.
 app = typer.Typer()
+
+# app_version will be set from git tag.
 app_version = importlib.metadata.version("tsoppy")
 
 
@@ -19,17 +35,82 @@ def version():
     print(f"tsoppy version {app_version}")
 
 
+def glob_pattern_callback(value: str) -> str:
+    """
+    Callback function checking that the glob pattern ends with '.vcf'.
+    """
+    if not value.endswith(".vcf"):
+        raise typer.BadParameter("Glob pattern must end with '.vcf'.")
+    return value
+
+
+def inpred_id_regex_callback(value: str) -> str:
+    """
+    Callback function ensuring inpred_id_regex contains the required named capture groups.
+    """
+    if "<patient_id>" not in value:
+        raise typer.BadParameter(
+            "inpred_id_regex must contain a named group 'patient_id'."
+        )
+    if "<sample_type>" not in value:
+        raise typer.BadParameter(
+            "inpred_id_regex must contain a named group 'sample_type'."
+        )
+    return value
+
+
+def tumor_sample_types_callback(value: str) -> str:
+    """
+    Callback function to ensure tumor_sample_types is a comma-separated list of single letters.
+    """
+    if not re.fullmatch(r"^([A-Za-z],)+[A-Za-z]$", value):
+        raise typer.BadParameter(
+            "tumor_sample_types must be comma-separated list of single letters."
+        )
+    return value
+
+
 @app.command()
-def placeholder(
-    user_name: Annotated[str, typer.Option("--name", "-n")],
-    user_id: Annotated[str, typer.Option("--id", "-i")],
-    verbose: Annotated[bool, typer.Option("--verbose", "-v")] = False,
+def update_small_variant_vcf_list(
+    results_dir: Annotated[
+        Path | None,
+        typer.Option(
+            help="Directory where the results of the latest TSO500 run are stored."
+        ),
+    ],
+    glob_pattern: Annotated[
+        str,
+        typer.Option(
+            help="Glob pattern to search for small variant VCF files in the results directory.",
+            callback=glob_pattern_callback,
+        ),
+    ] = "**/Results/**/*_MergedSmallVariants.genome.vcf",
+    inpred_id_regex: Annotated[
+        str,
+        typer.Option(
+            help="Regular expression to extract the inpred_id from the VCF file name.",
+            callback=inpred_id_regex_callback,
+        ),
+    ] = "(?P<patient_id>\D{3}\d{4})-\D\d{2}-(?P<sample_type>\D)\d{2}-\D\d{2}.*.vcf$",
+    output: Annotated[
+        str, typer.Option(help="Name of new small variant VCF list.")
+    ] = "small_variant_vcf_list_<YYYYMMDD>.tsv",
+    tumor_sample_types: Annotated[
+        str,
+        typer.Option(
+            help="Comma-separated list of sample types that are considered tumor samples."
+        ),
+    ] = "C,D,d,L,M,P,p,R,r,T,X",
+    vcf_list: Annotated[
+        Path | None, typer.Option(help="Path to list of small variant VCF files.")
+    ] = None,
 ):
     """
-    This is the helptext for the placeholder command that demonstrates how to
-    use Typer for CLI applications.
+    Updates the small variant VCF list based on VCF(s) in results directory.
     """
-    if verbose:
-        print(f"{user_name} has the following id: {user_id}")
-    else:
-        print(f"{user_name}: {user_id}")
+    logger.info("Start updating small variant VCF list.")
+    small_variant_vcf_list = VcfList(
+        results_dir, glob_pattern, vcf_list, inpred_id_regex, tumor_sample_types, output
+    )
+    small_variant_vcf_list.update()
+    logger.info("Finished updating small variant VCF list.")
diff --git a/src/tsoppy/update_small_variant_vcf_list/__init__.py b/src/tsoppy/update_small_variant_vcf_list/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/tsoppy/update_small_variant_vcf_list/main.py b/src/tsoppy/update_small_variant_vcf_list/main.py
new file mode 100644
index 0000000..6065c2d
--- /dev/null
+++ b/src/tsoppy/update_small_variant_vcf_list/main.py
@@ -0,0 +1,212 @@
+"""
+This module defines the classes 'VcfList' and 'Vcf'.
+'VcfList' takes a directory holding TSO500 results, a glob to identify small variant vcf files, the currect small variant vcf list,
+a regular expression matching InPreD IDs, a set of tumor sample types and the path to the new small variant vcf list.
+'VcfList' has a method to update the current small variant vcf list with vcfs found in the TSO500 results directory.
+'Vcf' is defined by a path to a small variant vcf and a set of tumor sample types.
+'Vcf' provides a method to create a new row for a pandas dataframe.
+"""
+
+import glob
+import logging
+import re
+from datetime import datetime
+from pathlib import Path
+
+import polars
+
+# Use logger that was set up in CLI
+logger = logging.getLogger(__name__)
+
+
+class InvalidSampleType(Exception):
+    """
+    Exception if sample type is not valid.
+    """
+
+    def __init__(self, msg="sample type is not valid"):
+        self.msg = msg
+        super().__init__(self.msg)
+
+    def __str__(self):
+        return self.msg
+
+
+class VcfList:
+    """
+    Represents small variant VCF list.
+
+    Attributes:
+        dataframe (Dataframe): Dataframe representing the current version of small variant VCF list.
+        inpred_id_regex (str): Regular expression matching InPreD IDs.
+        output (str): Path to updated version of small variant VCF list.
+        tumor_sample_types (set[str]): Single letter codes representing a tumor sample.
+        vcf_list_columns (list[str]): List of dataframe column names.
+        vcfs (dict): Small variant VCF(s) located in TSO500 results directory.
+    """
+
+    vcf_list_columns = {"vcf": polars.String, "sample_type": polars.String}
+
+    def __init__(
+        self,
+        results_dir: Path,
+        glob_pattern: str,
+        vcf_list: Path | None,
+        inpred_id_regex: str,
+        tumor_sample_types: str,
+        output: str,
+    ):
+        """
+        Create new instance of SmallVariantVcfList.
+        """
+        self.vcfs = glob.glob(f"{results_dir}/{glob_pattern}")
+        self.inpred_id_regex = rf"{inpred_id_regex}"
+        self.tumor_sample_types = set(tumor_sample_types.split(","))
+        self.dataframe = polars.DataFrame(schema=self.vcf_list_columns)
+
+        # Try reading small variant VCF list or start from scratch
+        if vcf_list:
+            try:
+                self.dataframe = polars.read_csv(
+                    source=vcf_list,
+                    separator="\t",
+                    schema=self.vcf_list_columns,
+                    ignore_errors=True,
+                    has_header=False,
+                    raise_if_empty=False,
+                )
+            except FileNotFoundError:
+                logger.warning(
+                    f"{vcf_list} not found, creating new small variant VCF list."
+                )
+        else:
+            logger.info("no small variant VCF list specified, creating new one.")
+
+        # Replace placeholder with actual date
+        if "<YYYYMMDD>" in output:
+            now = datetime.now()
+            self.output = output.replace("<YYYYMMDD>", now.strftime("%Y%m%d"))
+        else:
+            self.output = output
+
+    def __eq__(self, other):
+        """
+        Compare to other class instance.
+        """
+        if not isinstance(other, VcfList):
+            return NotImplemented
+        if self.dataframe != other.dataframe:
+            return False
+        if self.inpred_id_regex != other.inpred_id_regex:
+            return False
+        if self.output != other.output:
+            return False
+        if self.tumor_sample_types != other.tumor_sample_types:
+            return False
+        return self.vcfs != other.vcfs
+
+    def update(self):
+        """
+        Add VCF(s) from results directory to small variant VCF list.
+        """
+
+        # Loop over all small variant VCFs
+        for vcf in self.vcfs:
+            # Try to create vcf class instance
+            try:
+                small_variant_vcf = Vcf(
+                    vcf, self.inpred_id_regex, self.tumor_sample_types
+                )
+            except AttributeError:
+                logger.warning(
+                    f"could not parse InPreD ID from {small_variant_vcf.vcf}, skipping."
+                )
+                continue
+            except InvalidSampleType:
+                logger.warning(
+                    f"{small_variant_vcf.vcf} has sample type {small_variant_vcf.sample_type} which is not {self.tumor_sample_types} or N(ormal), skipping."
+                )
+                continue
+
+            # Avoid duplication
+            if small_variant_vcf.vcf in self.dataframe["vcf"].to_list():
+                logger.warning(f"{vcf} is already in small variant VCF list, skipping.")
+                continue
+
+            # Exclude control samples
+            if small_variant_vcf.patient_id.startswith("IPC"):
+                logger.warning(
+                    f"{small_variant_vcf.patient_id} is a control sample, skipping."
+                )
+                continue
+
+            # Add vcf to list
+            self.dataframe = polars.concat([self.dataframe, small_variant_vcf.row()])
+
+            # Check if new patient ID is represented multiple times
+            patient_sample_count = (
+                self.dataframe["vcf"] == small_variant_vcf.patient_id
+            ).sum()
+            if patient_sample_count > 1:
+                logger.warning(
+                    f"patient {small_variant_vcf.patient_id} has {patient_sample_count} vcf(s) in the small variant VCF list."
+                )
+
+        # Write updated small variant VCF list to file
+        self.dataframe.unique().write_csv(
+            file=self.output, separator="\t", include_header=False
+        )
+
+
+class Vcf:
+    """
+    Represents small variant VCF.
+
+    Attributes:
+        patient_id (str): ID of patient that the VCF belongs to.
+        sample_type (str): Single letter code representing type of sample, e.g. T = tumor.
+        vcf (str): Path to VCF file.
+    """
+
+    def __init__(self, vcf: str, inpred_id_regex: str, tumor_sample_types: set):
+        """
+        Create new instance of SmallVariantVcf.
+        """
+        self.vcf = vcf
+
+        # Parse InPreD ID to get patient ID and sample type
+        match = re.search(inpred_id_regex, self.vcf)
+        try:
+            self.patient_id = match.group("patient_id")
+            self.sample_type = match.group("sample_type")
+        except AttributeError:
+            raise AttributeError
+
+        # Validate sample type is N(ormal) or included in tumor_sample_types
+        if self.sample_type != "N":
+            if self.sample_type not in tumor_sample_types:
+                raise InvalidSampleType
+            else:
+                # Reset any sample type in tumor_sample_types with T
+                logger.warning(
+                    f"sample type code {self.sample_type} for {self.vcf} will be replaced with T"
+                )
+                self.sample_type = "T"
+
+    def __eq__(self, other):
+        """
+        Compare to other class instance.
+        """
+        if not isinstance(other, Vcf):
+            return NotImplemented
+        if self.patient_id != other.patient_id:
+            return False
+        if self.sample_type != other.sample_type:
+            return False
+        return self.vcf != other.vcf
+
+    def row(self):
+        """
+        Return small variant VCF list row.
+        """
+        return polars.DataFrame({"vcf": [self.vcf], "sample_type": [self.sample_type]})
diff --git a/tests/cli_test.py b/tests/cli_test.py
deleted file mode 100644
index 7b8ee75..0000000
--- a/tests/cli_test.py
+++ /dev/null
@@ -1,10 +0,0 @@
-"""
-CLI module unit tests for tsoppy.
-"""
-
-
-def test_placeholder():
-    """
-    Unit test for the placeholder command in the CLI module.
-    """
-    assert True
diff --git a/tests/test_data/update_small_variant_vcf_list_main/create_new_small_variant_vcf_list/LocalApp/Results/IPH0001-D01-N01-A01/IPH0001-D01-N01-A01_MergedSmallVariants.genome.vcf b/tests/test_data/update_small_variant_vcf_list_main/create_new_small_variant_vcf_list/LocalApp/Results/IPH0001-D01-N01-A01/IPH0001-D01-N01-A01_MergedSmallVariants.genome.vcf
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_data/update_small_variant_vcf_list_main/create_new_small_variant_vcf_list/TSO500_vcf_list_expected.tsv b/tests/test_data/update_small_variant_vcf_list_main/create_new_small_variant_vcf_list/TSO500_vcf_list_expected.tsv
new file mode 100644
index 0000000..2de322d
--- /dev/null
+++ b/tests/test_data/update_small_variant_vcf_list_main/create_new_small_variant_vcf_list/TSO500_vcf_list_expected.tsv
@@ -0,0 +1 @@
+tests/test_data/update_small_variant_vcf_list_main/create_new_small_variant_vcf_list/LocalApp/Results/IPH0001-D01-N01-A01/IPH0001-D01-N01-A01_MergedSmallVariants.genome.vcf	N
diff --git a/tests/test_data/update_small_variant_vcf_list_main/sample_is_control/LocalApp/Results/IPC0002-D01-N01-A01/IPC0002-D01-N01-A01_MergedSmallVariants.genome.vcf b/tests/test_data/update_small_variant_vcf_list_main/sample_is_control/LocalApp/Results/IPC0002-D01-N01-A01/IPC0002-D01-N01-A01_MergedSmallVariants.genome.vcf
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_data/update_small_variant_vcf_list_main/sample_is_control/TSO500_vcf_list.tsv b/tests/test_data/update_small_variant_vcf_list_main/sample_is_control/TSO500_vcf_list.tsv
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_data/update_small_variant_vcf_list_main/sample_is_control/TSO500_vcf_list_expected.tsv b/tests/test_data/update_small_variant_vcf_list_main/sample_is_control/TSO500_vcf_list_expected.tsv
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_data/update_small_variant_vcf_list_main/skip_existing_vcf/LocalApp/Results/IPH0001-D01-N01-A01/IPH0001-D01-N01-A01_MergedSmallVariants.genome.vcf b/tests/test_data/update_small_variant_vcf_list_main/skip_existing_vcf/LocalApp/Results/IPH0001-D01-N01-A01/IPH0001-D01-N01-A01_MergedSmallVariants.genome.vcf
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_data/update_small_variant_vcf_list_main/skip_existing_vcf/TSO500_vcf_list.tsv b/tests/test_data/update_small_variant_vcf_list_main/skip_existing_vcf/TSO500_vcf_list.tsv
new file mode 100644
index 0000000..166d2a7
--- /dev/null
+++ b/tests/test_data/update_small_variant_vcf_list_main/skip_existing_vcf/TSO500_vcf_list.tsv
@@ -0,0 +1 @@
+tests/test_data/update_small_variant_vcf_list_main/skip_existing_vcf/LocalApp/Results/IPH0001-D01-N01-A01/IPH0001-D01-N01-A01_MergedSmallVariants.genome.vcf	N
diff --git a/tests/test_data/update_small_variant_vcf_list_main/skip_existing_vcf/TSO500_vcf_list_expected.tsv b/tests/test_data/update_small_variant_vcf_list_main/skip_existing_vcf/TSO500_vcf_list_expected.tsv
new file mode 100644
index 0000000..166d2a7
--- /dev/null
+++ b/tests/test_data/update_small_variant_vcf_list_main/skip_existing_vcf/TSO500_vcf_list_expected.tsv
@@ -0,0 +1 @@
+tests/test_data/update_small_variant_vcf_list_main/skip_existing_vcf/LocalApp/Results/IPH0001-D01-N01-A01/IPH0001-D01-N01-A01_MergedSmallVariants.genome.vcf	N
diff --git a/tests/test_data/update_small_variant_vcf_list_main/small_variant_vcf_list_does_not_exist/LocalApp/Results/IPH0001-D01-N01-A01/IPH0001-D01-N01-A01_MergedSmallVariants.genome.vcf b/tests/test_data/update_small_variant_vcf_list_main/small_variant_vcf_list_does_not_exist/LocalApp/Results/IPH0001-D01-N01-A01/IPH0001-D01-N01-A01_MergedSmallVariants.genome.vcf
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_data/update_small_variant_vcf_list_main/small_variant_vcf_list_does_not_exist/TSO500_vcf_list_expected.tsv b/tests/test_data/update_small_variant_vcf_list_main/small_variant_vcf_list_does_not_exist/TSO500_vcf_list_expected.tsv
new file mode 100644
index 0000000..91a1e5c
--- /dev/null
+++ b/tests/test_data/update_small_variant_vcf_list_main/small_variant_vcf_list_does_not_exist/TSO500_vcf_list_expected.tsv
@@ -0,0 +1 @@
+tests/test_data/update_small_variant_vcf_list_main/small_variant_vcf_list_does_not_exist/LocalApp/Results/IPH0001-D01-N01-A01/IPH0001-D01-N01-A01_MergedSmallVariants.genome.vcf	N
diff --git a/tests/test_data/update_small_variant_vcf_list_main/successfully_update_small_variant_vcf_list/LocalApp/Results/IPH0001-D01-N01-A01/IPH0001-D01-N01-A01_MergedSmallVariants.genome.vcf b/tests/test_data/update_small_variant_vcf_list_main/successfully_update_small_variant_vcf_list/LocalApp/Results/IPH0001-D01-N01-A01/IPH0001-D01-N01-A01_MergedSmallVariants.genome.vcf
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_data/update_small_variant_vcf_list_main/successfully_update_small_variant_vcf_list/TSO500_vcf_list.tsv b/tests/test_data/update_small_variant_vcf_list_main/successfully_update_small_variant_vcf_list/TSO500_vcf_list.tsv
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_data/update_small_variant_vcf_list_main/successfully_update_small_variant_vcf_list/TSO500_vcf_list_expected.tsv b/tests/test_data/update_small_variant_vcf_list_main/successfully_update_small_variant_vcf_list/TSO500_vcf_list_expected.tsv
new file mode 100644
index 0000000..682e578
--- /dev/null
+++ b/tests/test_data/update_small_variant_vcf_list_main/successfully_update_small_variant_vcf_list/TSO500_vcf_list_expected.tsv
@@ -0,0 +1 @@
+tests/test_data/update_small_variant_vcf_list_main/successfully_update_small_variant_vcf_list/LocalApp/Results/IPH0001-D01-N01-A01/IPH0001-D01-N01-A01_MergedSmallVariants.genome.vcf	N
diff --git a/tests/test_update_small_variant_vcf_list_main.py b/tests/test_update_small_variant_vcf_list_main.py
new file mode 100644
index 0000000..e912965
--- /dev/null
+++ b/tests/test_update_small_variant_vcf_list_main.py
@@ -0,0 +1,208 @@
+"""
+update small variant vcf list subpackage main module unit tests.
+"""
+
+import filecmp
+import os
+import unittest
+from contextlib import nullcontext
+from os import path
+
+import polars
+import pytest
+
+from tsoppy.update_small_variant_vcf_list.main import InvalidSampleType, Vcf, VcfList
+
+# Define path to test data - cannot be absolute due to different paths locally and in CI
+test_data_dir = "tests/test_data/update_small_variant_vcf_list_main"
+
+# test constants
+glob_pattern = "**/Results/**/*_MergedSmallVariants.genome.vcf"
+tumor_sample_types = "C,D,d,L,M,P,p,R,r,T,X"
+inpred_id_regex = (
+    "(?P<patient_id>\\D{3}\\d{4})-\\D\\d{2}-(?P<sample_type>\\D)\\d{2}-\\D\\d{2}.*.vcf$"
+)
+
+
+class TestVcfList(unittest.TestCase):
+    def test_update(self):
+        test_cases = [
+            {
+                "name": "successfully update small variant vcf list",
+                "results_dir": path.join(
+                    test_data_dir, "successfully_update_small_variant_vcf_list"
+                ),
+                "glob_pattern": glob_pattern,
+                "vcf_list": path.join(
+                    test_data_dir,
+                    "successfully_update_small_variant_vcf_list/TSO500_vcf_list.tsv",
+                ),
+                "inpred_id_regex": inpred_id_regex,
+                "tumor_sample_types": tumor_sample_types,
+                "output": path.join(
+                    test_data_dir,
+                    "successfully_update_small_variant_vcf_list/TSO500_vcf_list_updated.tsv",
+                ),
+                "expected": path.join(
+                    test_data_dir,
+                    "successfully_update_small_variant_vcf_list/TSO500_vcf_list_expected.tsv",
+                ),
+            },
+            {
+                "name": "create new small variant vcf list",
+                "results_dir": path.join(
+                    test_data_dir, "create_new_small_variant_vcf_list"
+                ),
+                "glob_pattern": glob_pattern,
+                "vcf_list": None,
+                "inpred_id_regex": inpred_id_regex,
+                "tumor_sample_types": tumor_sample_types,
+                "output": path.join(
+                    test_data_dir,
+                    "create_new_small_variant_vcf_list/TSO500_vcf_list_updated.tsv",
+                ),
+                "expected": path.join(
+                    test_data_dir,
+                    "create_new_small_variant_vcf_list/TSO500_vcf_list_expected.tsv",
+                ),
+            },
+            {
+                "name": "small variant vcf list does not exist",
+                "results_dir": path.join(
+                    test_data_dir, "small_variant_vcf_list_does_not_exist"
+                ),
+                "glob_pattern": glob_pattern,
+                "vcf_list": path.join(
+                    test_data_dir,
+                    "small_variant_vcf_list_does_not_exist/TSO500_vcf_list.tsv",
+                ),
+                "inpred_id_regex": inpred_id_regex,
+                "tumor_sample_types": tumor_sample_types,
+                "output": path.join(
+                    test_data_dir,
+                    "small_variant_vcf_list_does_not_exist/TSO500_vcf_list_updated.tsv",
+                ),
+                "expected": path.join(
+                    test_data_dir,
+                    "small_variant_vcf_list_does_not_exist/TSO500_vcf_list_expected.tsv",
+                ),
+            },
+            {
+                "name": "skip existing vcf",
+                "results_dir": path.join(test_data_dir, "skip_existing_vcf"),
+                "glob_pattern": glob_pattern,
+                "vcf_list": path.join(
+                    test_data_dir, "skip_existing_vcf/TSO500_vcf_list.tsv"
+                ),
+                "inpred_id_regex": inpred_id_regex,
+                "tumor_sample_types": tumor_sample_types,
+                "output": path.join(
+                    test_data_dir, "skip_existing_vcf/TSO500_vcf_list_updated.tsv"
+                ),
+                "expected": path.join(
+                    test_data_dir, "skip_existing_vcf/TSO500_vcf_list_expected.tsv"
+                ),
+            },
+            {
+                "name": "sample is control",
+                "results_dir": path.join(test_data_dir, "sample_is_control"),
+                "glob_pattern": glob_pattern,
+                "vcf_list": path.join(
+                    test_data_dir, "sample_is_control/TSO500_vcf_list.tsv"
+                ),
+                "inpred_id_regex": inpred_id_regex,
+                "tumor_sample_types": tumor_sample_types,
+                "output": path.join(
+                    test_data_dir, "sample_is_control/TSO500_vcf_list_updated.tsv"
+                ),
+                "expected": path.join(
+                    test_data_dir, "sample_is_control/TSO500_vcf_list_expected.tsv"
+                ),
+            },
+        ]
+
+        for test_case in test_cases:
+            with self.subTest(msg=test_case["name"]):
+                got = VcfList(
+                    test_case["results_dir"],
+                    test_case["glob_pattern"],
+                    test_case["vcf_list"],
+                    test_case["inpred_id_regex"],
+                    test_case["tumor_sample_types"],
+                    test_case["output"],
+                )
+                got.update()
+                assert filecmp.cmp(test_case["output"], test_case["expected"])
+                os.remove(test_case["output"])
+
+
+class TestVcf(unittest.TestCase):
+    def test_init(self):
+        test_cases = [
+            {
+                "name": "include sample",
+                "vcf": "IPH0001-D01-T01-A01_MergedSmallVariants.genome.vcf",
+                "inpred_id_regex": inpred_id_regex,
+                "tumor_sample_types": tumor_sample_types,
+                "exception": nullcontext(),
+                "patient_id": "IPH0001",
+                "sample_type": "T",
+            },
+            {
+                "name": "inpred id is not parsable",
+                "vcf": "IPH0001D01-T01-A01_MergedSmallVariants.genome.vcf",
+                "inpred_id_regex": inpred_id_regex,
+                "tumor_sample_types": tumor_sample_types,
+                "exception": pytest.raises(AttributeError),
+                "patient_id": None,
+                "sample_type": None,
+            },
+            {
+                "name": "sample is neither tumor nor normal",
+                "vcf": "IPH0001-D01-A01-A01_MergedSmallVariants.genome.vcf",
+                "inpred_id_regex": inpred_id_regex,
+                "tumor_sample_types": tumor_sample_types,
+                "exception": pytest.raises(InvalidSampleType),
+                "patient_id": "IPH0001",
+                "sample_type": "A",
+            },
+        ]
+
+        for test_case in test_cases:
+            with self.subTest(msg=test_case["name"]):
+                with test_case["exception"]:
+                    got = Vcf(
+                        test_case["vcf"],
+                        test_case["inpred_id_regex"],
+                        test_case["tumor_sample_types"],
+                    )
+                    assert got.patient_id == test_case["patient_id"]
+                    assert got.sample_type == test_case["sample_type"]
+
+    def test_row(self):
+        test_cases = [
+            {
+                "name": "successfully return row",
+                "vcf": "IPH0001-D01-T01-A01_MergedSmallVariants.genome.vcf",
+                "inpred_id_regex": inpred_id_regex,
+                "patient_id": "IPH0001",
+                "sample_type": "T",
+                "tumor_sample_types": tumor_sample_types,
+                "expected": polars.DataFrame(
+                    {
+                        "vcf": ["IPH0001-D01-T01-A01_MergedSmallVariants.genome.vcf"],
+                        "sample_type": ["T"],
+                    }
+                ),
+            },
+        ]
+
+        for test_case in test_cases:
+            with self.subTest(msg=test_case["name"]):
+                vcf = Vcf(
+                    test_case["vcf"],
+                    test_case["inpred_id_regex"],
+                    test_case["tumor_sample_types"],
+                )
+                got = vcf.row()
+                assert got.equals(test_case["expected"])