diff --git a/docker-compose.test.yaml b/docker-compose.test.yaml
index f167171..bd585a0 100644
--- a/docker-compose.test.yaml
+++ b/docker-compose.test.yaml
@@ -20,7 +20,8 @@ services:
     command: /bin/bash -c '
       cd /tds &&
       /poetry_user_install_dev.bash &&
-      pytest -svv --cov=transcriptomics_data_service --cov-branch
+      pytest -svv --cov=transcriptomics_data_service --cov-branch &&
+      coverage html
       '
 
   tds-db:
diff --git a/tests/test_db.py b/tests/test_db.py
index f8f5dff..2dafec3 100644
--- a/tests/test_db.py
+++ b/tests/test_db.py
@@ -1,16 +1,84 @@
+from asyncpg import Connection, UniqueViolationError
 import pytest
 from transcriptomics_data_service.db import Database
-from transcriptomics_data_service.models import ExperimentResult
+from transcriptomics_data_service.models import ExperimentResult, GeneExpression
 
+TEST_EXPERIMENT_RESULT_ID = "test-experiment-id"
+TEST_EXPERIMENT_RESULT = ExperimentResult(
+    experiment_result_id=TEST_EXPERIMENT_RESULT_ID,
+    assembly_id="assembly_test_id",
+    assembly_name="assembly_test_name",
+)
+TEST_GENE_EXPRESSION = GeneExpression(
+    experiment_result_id=TEST_EXPERIMENT_RESULT_ID,
+    gene_code="test-gene-code",
+    sample_id="test-sample-id",
+    raw_count=90,
+)
 
+##########################
+# CRUD: experiment_results
+##########################
+
+
+@pytest.mark.asyncio
+async def test_create_read_experiment_result(db: Database, db_cleanup):
+    # exp_result = await _create_experiment_result(db)
+    await db.create_experiment_result(TEST_EXPERIMENT_RESULT)
+    db_exp_result = await db.read_experiment_result(TEST_EXPERIMENT_RESULT_ID)
+    assert TEST_EXPERIMENT_RESULT == db_exp_result
+
+
+@pytest.mark.asyncio
+async def test_update_experiment_result(db: Database, db_cleanup):
+    await db.create_experiment_result(TEST_EXPERIMENT_RESULT)
+    new_exp = TEST_EXPERIMENT_RESULT.model_copy()
+    new_exp.assembly_name = "updated_assembly_name"
+    await db.update_experiment_result(new_exp)
+    db_exp_result = await db.read_experiment_result(new_exp.experiment_result_id)
+    assert db_exp_result.assembly_name == new_exp.assembly_name
+
+
+@pytest.mark.asyncio
+async def test_delete_experiment_result(db: Database, db_cleanup):
+    await db.create_experiment_result(TEST_EXPERIMENT_RESULT)
+    await db.delete_experiment_result(TEST_EXPERIMENT_RESULT_ID)
+    db_exp_result = await db.read_experiment_result(TEST_EXPERIMENT_RESULT_ID)
+    assert db_exp_result == None
+
+
+########################
+# CRUD: gene_expressions
+########################
+
+
+@pytest.mark.asyncio
+async def test_gene_expression(db: Database, db_cleanup):
+    async with db.transaction_connection() as conn:
+        await db.create_experiment_result(TEST_EXPERIMENT_RESULT, conn)
+        await db.create_gene_expressions([TEST_GENE_EXPRESSION], conn)
+
+    # read all
+    db_expressions = await db.fetch_expressions()
+    assert len(db_expressions) == 1
+    assert db_expressions[0] == TEST_GENE_EXPRESSION
+
+    # read by ExperimentResult ID
+    db_expressions = await db.fetch_expressions(experiment_result_id=TEST_EXPERIMENT_RESULT_ID)
+    assert db_expressions[0] == TEST_GENE_EXPRESSION
+
+
+# TEST TRANSACTIONS
 @pytest.mark.asyncio
-async def test_create_experiment_result(db: Database, db_cleanup):
-    exp_id = "exp_test"
-    exp_result = ExperimentResult(
-        experiment_result_id=exp_id,
-        assembly_id="assembly_test_id",
-        assembly_name="assembly_test_name",
-    )
-    await db.create_experiment_result(exp_result)
-    db_exp_result = await db.read_experiment_result(exp_id)
-    assert exp_result == db_exp_result
+async def test_transaction(db: Database, db_cleanup):
+    async with db.transaction_connection() as conn:
+        try:
+            await db.create_experiment_result(TEST_EXPERIMENT_RESULT, conn)
+            await db.create_gene_expressions([TEST_GENE_EXPRESSION, TEST_GENE_EXPRESSION], conn)
+            assert False
+        except:
+            assert True
+    db_exp = await db.read_experiment_result(TEST_EXPERIMENT_RESULT_ID)
+    db_gene_expr = await db.fetch_expressions()
+    assert db_exp == None
+    assert len(db_gene_expr) == 0
diff --git a/transcriptomics_data_service/db.py b/transcriptomics_data_service/db.py
index bdf3307..a9b76f2 100644
--- a/transcriptomics_data_service/db.py
+++ b/transcriptomics_data_service/db.py
@@ -91,10 +91,8 @@ async def create_gene_expressions(self, expressions: list[GeneExpression], trans
         Rows on gene_expressions can only be created as part of an RCM ingestion.
         Ingestion is all-or-nothing, hence the transaction.
         """
-        async with transaction_conn.transaction():
-            # sub-transaction
-            for gene_expression in expressions:
-                await self._create_gene_expression(gene_expression, transaction_conn)
+        for gene_expression in expressions:
+            await self._create_gene_expression(gene_expression, transaction_conn)
 
     async def _create_gene_expression(self, expression: GeneExpression, transaction_conn: asyncpg.Connection):
         # Creates a row on gene_expressions within a transaction.
@@ -112,15 +110,15 @@ async def _create_gene_expression(self, expression: GeneExpression, transaction_
             expression.tmm_count,
         )
 
-    async def fetch_expressions(self) -> tuple[GeneExpression, ...]:
-        return tuple([r async for r in self._select_expressions(None)])
+    async def fetch_expressions(self, experiment_result_id: str | None = None) -> tuple[GeneExpression, ...]:
+        return tuple([r async for r in self._select_expressions(exp_id=experiment_result_id)])
 
     async def _select_expressions(self, exp_id: str | None) -> AsyncIterator[GeneExpression]:
         conn: asyncpg.Connection
         where_clause = "WHERE experiment_result_id = $1" if exp_id is not None else ""
         query = f"SELECT * FROM gene_expressions {where_clause}"
         async with self.connect() as conn:
-            res = await conn.fetch(query, *((exp_id) if exp_id is not None else ()))
+            res = await conn.fetch(query, *((exp_id,) if exp_id is not None else ()))
         for r in map(lambda g: self._deserialize_gene_expression(g), res):
             yield r