accrual: Filter opening balance txn before main reporting.

So far we've been implicitly relying on this by the user passing search
terms that filter out the opening balance transaction. That will stop
happening with the aging report, so we need to do it ourselves.

conservancy_beancount/reports/accrual.py

@@ -498,6 +498,7 @@ def main(arglist: Optional[Sequence[str]]=None,
             'lineno': 1,
         }
         load_errors = [Error(source, "no books to load in configuration", None)]
+    filters.remove_opening_balance_txn(entries)
     postings = filter_search(data.Posting.from_entries(entries), args.search_terms)
     groups: PostGroups = dict(AccrualPostings.group_by_meta(postings, 'invoice'))
     groups = AccrualAccount.filter_paid_accruals(groups) or groups

tests/books/accruals.beancount

@@ -5,6 +5,12 @@
 2020-01-01 open Expenses:Travel
 2020-01-01 open Income:Donations
 2020-01-01 open Liabilities:Payable:Accounts
+2020-01-01 open Equity:Funds:Opening
+
+2020-03-01 * "Opening balances"
+  Equity:Funds:Opening  -1000 USD
+  Assets:Receivable:Accounts  6000 USD
+  Liabilities:Payable:Accounts  -5000 USD
 
 2020-03-05 * "EarlyBird" "Payment for receivable from previous FY"
   rt-id: "rt:40"
@@ -24,6 +30,13 @@
   Liabilities:Payable:Accounts  -75 USD
   Expenses:Travel  75 USD
 
+2020-04-30 ! "Vendor" "Travel reimbursement"
+  rt-id: "rt:310"
+  contract: "rt:310/3100"
+  invoice: "FIXME"  ; still waiting on them to send it
+  Liabilities:Payable:Accounts  -200 USD
+  Expenses:Travel  200 USD
+
 2020-05-05 * "DonorA" "Donation pledge"
   rt-id: "rt:505"
   invoice: "rt:505/5050"

tests/test_reports_accrual.py

@@ -33,10 +33,15 @@ from conservancy_beancount.reports import accrual
 from conservancy_beancount.reports import core
 
 _accruals_load = bc_loader.load_file(testutil.test_path('books/accruals.beancount'))
+ACCRUAL_TXNS = [
+    entry for entry in _accruals_load[0]
+    if hasattr(entry, 'narration')
+    and entry.narration != 'Opening balances'
+]
 ACCRUALS_COUNT = sum(
     1
-    for entry in _accruals_load[0]
-    for post in getattr(entry, 'postings', ())
+    for txn in ACCRUAL_TXNS
+    for post in txn.postings
     if post.account.startswith(('Assets:Receivable:', 'Liabilities:Payable:'))
 )
 
@@ -74,14 +79,9 @@ class RTClient(testutil.RTClient):
     }
 
 
-@pytest.fixture
-def accrual_entries():
-    return copy.deepcopy(_accruals_load[0])
-
 @pytest.fixture
 def accrual_postings():
-    entries = copy.deepcopy(_accruals_load[0])
-    return data.Posting.from_entries(entries)
+    return data.Posting.from_entries(copy.deepcopy(ACCRUAL_TXNS))
 
 def check_link_regexp(regexp, match_s, first_link_only=False):
     assert regexp