bug(session): Allow only valid state transitions

internal/db/sqltest/tests/session/invalid_state_transition.sql

@@ -0,0 +1,43 @@
+begin;
+    select plan(12);
+
+    -- Ensure session state table is populated
+    select is(count(*), 1::bigint) from session_state where session_id = 's1_____clare' and state='pending';
+    select is(count(*), 1::bigint) from session_state where session_id = 's1_____cindy' and state='terminated';
+    select is(count(*), 1::bigint) from session_state where session_id = 's1_____ciara' and state='canceling';
+    select is(count(*), 1::bigint) from session_state where session_id = 's1_____carly' and state='active';
+
+    -- Invalid duplicate state
+    select throws_ok($$ insert into session_state  ( session_id, state )
+        values  ('s1_____clare','pending')$$);
+
+    -- Invalid state transition from terminated to pending
+    select throws_ok($$ insert into session_state  ( session_id, state)
+        values  ('s1______cindy','pending')$$);
+
+    -- Invalid state transition from terminated to active
+    select throws_ok($$ insert into session_state  ( session_id, state)
+        values  ('s1______cindy','active')$$);
+
+    -- Invalid state transition from terminated to canceling
+    select throws_ok($$ insert into session_state  ( session_id, state)
+        values  ('s1______cindy','canceling')$$);
+
+    -- Invalid state transition from terminated to terminated
+    select throws_ok($$ insert into session_state  ( session_id, state)
+        values  ('s1______cindy','terminated')$$);
+
+    -- Invalid state transition from active to pending
+    select throws_ok($$ insert into session_state  ( session_id, state)
+        values  ('s1______carly','pending')$$);
+
+    -- Invalid state transition from canceling to pending
+    select throws_ok($$ insert into session_state  ( session_id, state)
+        values  ('s1______ciara','pending')$$);
+
+    -- Invalid state transition from canceling to active
+    select throws_ok($$ insert into session_state  ( session_id, state)
+        values  ('s1______ciara','active')$$);
+
+    select * from finish();
+rollback;