Timestream: fix ListTables logic (#8634)

Author: jerryhxu

moto/timestreamwrite/models.py

@@ -217,8 +217,14 @@ def describe_table(self, database_name: str, table_name: str) -> TimestreamTable
         return database.describe_table(table_name)
 
     def list_tables(self, database_name: str) -> Iterable[TimestreamTable]:
-        database = self.describe_database(database_name)
-        return database.list_tables()
+        if database_name is None:
+            tables = (
+                table for db in self.list_databases() for table in db.list_tables()
+            )
+        else:
+            database = self.describe_database(database_name)
+            tables = database.list_tables()
+        return tables
 
     def update_table(
         self,

tests/test_timestreamwrite/test_timestreamwrite_table.py

@@ -198,6 +198,39 @@ def test_create_multiple_tables():
     assert {t["TableStatus"] for t in tables} == {"ACTIVE"}
 
 
+@mock_aws
+def test_list_tables_without_database():
+    ts = boto3.client("timestream-write", region_name="us-east-1")
+    ts.create_database(DatabaseName="mydatabase")
+
+    for idx in range(0, 5):
+        ts.create_table(
+            DatabaseName="mydatabase",
+            TableName=f"mytable_{idx}",
+            RetentionProperties={
+                "MemoryStoreRetentionPeriodInHours": 7,
+                "MagneticStoreRetentionPeriodInDays": 42,
+            },
+        )
+
+    database = ts.describe_database(DatabaseName="mydatabase")["Database"]
+
+    assert database["TableCount"] == 5
+
+    # database_name is optional in api call
+    tables = ts.list_tables()["Tables"]
+    assert len(tables) == 5
+    assert {t["DatabaseName"] for t in tables} == {"mydatabase"}
+    assert {t["TableName"] for t in tables} == {
+        "mytable_0",
+        "mytable_1",
+        "mytable_2",
+        "mytable_3",
+        "mytable_4",
+    }
+    assert {t["TableStatus"] for t in tables} == {"ACTIVE"}
+
+
 @mock_aws
 def test_delete_table():
     ts = boto3.client("timestream-write", region_name="us-east-1")