diff --git a/tests/py/test_payment_instruction_api.py b/tests/py/test_payment_instruction_api.py
new file mode 100644
index 0000000000..d043943fc0
--- /dev/null
+++ b/tests/py/test_payment_instruction_api.py
@@ -0,0 +1,199 @@
+import json
+
+from gratipay.testing import Harness
+
+class TestPaymentInstructionApi(Harness):
+
+    def test_get_with_team_filter(self):
+        "Test that GET with team_slug passed returns correct response."
+
+        alice = self.make_participant("alice", claimed_time='now')
+        gratipay = self.make_team("gratipay", is_approved=True)
+        gittip = self.make_team("gittip", is_approved=True)
+
+        alice.set_payment_instruction(gratipay, '10.0')
+        alice.set_payment_instruction(gittip, '12.0')
+
+        data = json.loads(self.client.GET(
+             "~/alice/payment-instruction.json?team_slug=" + gratipay.slug
+            , auth_as='alice').body)
+
+        assert data['team_slug'] == gratipay.slug
+        assert data['team_name'] == gratipay.name
+        assert data['amount'] == '10.00'
+        assert 'ctime' in data
+        assert 'mtime' in data
+        assert 'due' in data
+
+    def test_get_with_team_filter_raises_error_on_invalid_team_slug(self):
+        self.make_participant("alice", claimed_time = 'now')
+
+        response = self.client.GxT(
+             "~/alice/payment-instruction.json?team_slug=no-team"
+            , auth_as='alice')
+
+        assert response.code == 400
+
+    # pi => payment instruction.
+
+    def test_get_with_team_filter_returns_default_if_no_pi(self):
+        self.make_participant("alice", claimed_time='now')
+        gratipay = self.make_team("gratipay", is_approved=True)
+
+        data = json.loads(self.client.GET(
+             "~/alice/payment-instruction.json?team_slug=" + gratipay.slug
+            , auth_as='alice').body)
+
+        assert data['team_slug'] == gratipay.slug
+        assert data['team_name'] == gratipay.name
+        assert data['amount'] == '0.00'
+        assert data['due'] == '0.00'
+        assert data['ctime'] == None
+        assert data['mtime'] == None
+
+    def test_simple_get(self):
+        "Test that GET without any parameters returns correct response."
+
+        alice = self.make_participant("alice", claimed_time='now')
+        gratipay = self.make_team("gratipay", is_approved=True)
+        gittip = self.make_team("gittip", is_approved=True)
+
+        data = json.loads(self.client.GET(
+             "~/alice/payment-instruction.json", auth_as='alice').body)
+
+        assert len(data) == 0 # Empty 'array' should be returned.
+
+        alice.set_payment_instruction(gratipay, '10.0')
+        alice.set_payment_instruction(gittip, '12.0')
+
+        data = json.loads(self.client.GET(
+             "~/alice/payment-instruction.json", auth_as='alice').body)
+
+        assert len(data) == 2
+
+        assert data[0]['team_slug'] == gittip.slug # response is ordered by amount desc
+        assert data[0]['amount'] == '12.00'
+        assert data[0]['team_name'] == gittip.name
+
+        assert data[1]['team_slug'] == gratipay.slug
+        assert data[1]['amount'] == '10.00'
+        assert data[1]['team_name'] == gratipay.name
+
+        for d in data:
+            assert 'due' in d
+            assert 'ctime' in d
+            assert 'mtime' in d
+ 
+    def test_post(self):
+        "Test that POST to this endpoint works correctly."
+
+        self.make_participant("alice", claimed_time='now')
+        gratipay = self.make_team("gratipay", is_approved=True)
+        gittip = self.make_team("gittip", is_approved=True)
+
+        request_body = [
+            { 'amount': "1.50", 'team_slug': gratipay.slug },
+            { 'amount': "39.50", 'team_slug': gittip.slug }
+        ]
+
+        response = self.client.POST( "~/alice/payment-instruction.json"
+                                    , body=json.dumps(request_body)
+                                    , content_type='application/json'
+                                    , auth_as='alice')
+
+        assert response.code == 200
+
+        # Make sure apt response returned.
+        data = json.loads(response.body)
+
+        assert len(data) == 2
+
+        assert data[0]['team_slug'] == gratipay.slug
+        assert data[0]['team_name'] == gratipay.name
+        assert data[0]['amount'] == '1.50'
+
+        assert data[1]['team_slug'] == gittip.slug
+        assert data[1]['team_name'] == gittip.name
+        assert data[1]['amount'] == '39.50'
+
+        for d in data:
+            assert 'due' in d
+            assert 'ctime' in d
+            assert 'mtime' in d
+
+        # Make sure actually written to database.
+        data = json.loads(self.client.GET(
+             "~/alice/payment-instruction.json", auth_as='alice').body)
+
+        assert data[0]['team_slug'] == gittip.slug
+        assert data[0]['amount'] == '39.50'
+
+        assert data[1]['team_slug'] == gratipay.slug
+        assert data[1]['amount'] == '1.50'
+
+    def test_post_with_no_team_slug_key_returns_error(self):
+        self.make_participant("alice", claimed_time='now')
+
+        response = self.client.POST( "~/alice/payment-instruction.json"
+                                    , body=json.dumps([{ 'amount': "1.50" }])
+                                    , content_type='application/json'
+                                    , auth_as='alice')
+
+        assert response.code == 200 # Since batch processing.
+        assert 'error' in json.loads(response.body)[0]
+
+        data = json.loads(self.client.GET(
+             "~/alice/payment-instruction.json", auth_as='alice').body)
+        assert len(data) == 0
+
+    def test_post_with_no_amount_key_returns_error(self):
+        self.make_participant("alice", claimed_time='now')
+        gratipay = self.make_team("gratipay", is_approved=True)
+
+        response = self.client.POST( "~/alice/payment-instruction.json"
+                                    , body=json.dumps(
+                                        [{ 'team_slug': gratipay.slug }])
+                                    , content_type='application/json'
+                                    , auth_as='alice')
+
+        assert response.code == 200
+        assert 'error' in json.loads(response.body)[0]
+
+        data = json.loads(self.client.GET(
+             "~/alice/payment-instruction.json", auth_as='alice').body)
+        assert len(data) == 0
+
+    def test_adding_pi_for_invalid_team_returns_error(self):
+        self.make_participant("alice", claimed_time='now')
+
+        request_body = [{ 'team_slug': 'no-slug', 'amount': '39.50' }]
+
+        response = self.client.POST( "~/alice/payment-instruction.json"
+                                    , body=json.dumps(request_body)
+                                    , content_type='application/json'
+                                    , auth_as='alice')
+
+        assert response.code == 200
+        assert 'error' in json.loads(response.body)[0]
+
+        data = json.loads(self.client.GET(
+             "~/alice/payment-instruction.json", auth_as='alice').body)
+        assert len(data) == 0
+
+    def test_adding_pi_for_unapproved_team_returns_error(self):
+        self.make_participant("alice", claimed_time='now')
+        gratipay = self.make_team("gratipay", is_approved=False)
+
+        request_body = [{ 'team_slug': gratipay.slug, 'amount': '39.50' }]
+
+        response = self.client.POST( "~/alice/payment-instruction.json"
+                                    , body=json.dumps(request_body)
+                                    , content_type='application/json'
+                                    , auth_as='alice')
+
+        assert response.code == 200
+        assert 'error' in json.loads(response.body)[0]
+
+        data = json.loads(self.client.GET(
+             "~/alice/payment-instruction.json", auth_as='alice').body)
+        assert len(data) == 0