Fix README and basic startup example (#3275)

Follow-up of https://github.com/neondatabase/neon/pull/3270 which made
an example from main README.md not working.

Fixes that, by adding a way to specify a default tenant now and modifies
the basic neon_local test to start postgres and check branching.
Not all neon_local commands are implemented, so not all README.md
contents is tested yet.

test_runner/fixtures/neon_fixtures.py

@@ -18,6 +18,7 @@ from contextlib import closing, contextmanager
 from dataclasses import dataclass, field
 from enum import Flag, auto
 from functools import cached_property
+from itertools import chain, product
 from pathlib import Path
 from types import TracebackType
 from typing import Any, Dict, Iterator, List, Optional, Tuple, Type, Union, cast
@@ -1567,6 +1568,7 @@ class NeonCli(AbstractNeonCli):
         tenant_id: Optional[TenantId] = None,
         timeline_id: Optional[TimelineId] = None,
         conf: Optional[Dict[str, str]] = None,
+        set_default: bool = False,
     ) -> Tuple[TenantId, TimelineId]:
         """
         Creates a new tenant, returns its id and its initial timeline's id.
@@ -1575,47 +1577,51 @@ class NeonCli(AbstractNeonCli):
             tenant_id = TenantId.generate()
         if timeline_id is None:
             timeline_id = TimelineId.generate()
-        if conf is None:
-            res = self.raw_cli(
-                [
-                    "tenant",
-                    "create",
-                    "--tenant-id",
-                    str(tenant_id),
-                    "--timeline-id",
-                    str(timeline_id),
-                    "--pg-version",
-                    self.env.pg_version,
-                ]
-            )
-        else:
-            res = self.raw_cli(
-                [
-                    "tenant",
-                    "create",
-                    "--tenant-id",
-                    str(tenant_id),
-                    "--timeline-id",
-                    str(timeline_id),
-                    "--pg-version",
-                    self.env.pg_version,
-                ]
-                + sum(list(map(lambda kv: (["-c", kv[0] + ":" + kv[1]]), conf.items())), [])
+
+        args = [
+            "tenant",
+            "create",
+            "--tenant-id",
+            str(tenant_id),
+            "--timeline-id",
+            str(timeline_id),
+            "--pg-version",
+            self.env.pg_version,
+        ]
+        if conf is not None:
+            args.extend(
+                chain.from_iterable(
+                    product(["-c"], (f"{key}:{value}" for key, value in conf.items()))
+                )
             )
+        if set_default:
+            args.append("--set-default")
+
+        res = self.raw_cli(args)
         res.check_returncode()
         return tenant_id, timeline_id
 
+    def set_default(self, tenant_id: TenantId):
+        """
+        Update default tenant for future operations that require tenant_id.
+        """
+        res = self.raw_cli(["tenant", "set-default", "--tenant-id", str(tenant_id)])
+        res.check_returncode()
+
     def config_tenant(self, tenant_id: TenantId, conf: Dict[str, str]):
         """
         Update tenant config.
         """
-        if conf is None:
-            res = self.raw_cli(["tenant", "config", "--tenant-id", str(tenant_id)])
-        else:
-            res = self.raw_cli(
-                ["tenant", "config", "--tenant-id", str(tenant_id)]
-                + sum(list(map(lambda kv: (["-c", kv[0] + ":" + kv[1]]), conf.items())), [])
+
+        args = ["tenant", "config", "--tenant-id", str(tenant_id)]
+        if conf is not None:
+            args.extend(
+                chain.from_iterable(
+                    product(["-c"], (f"{key}:{value}" for key, value in conf.items()))
+                )
             )
+
+        res = self.raw_cli(args)
         res.check_returncode()
 
     def list_tenants(self) -> "subprocess.CompletedProcess[str]":
@@ -1650,36 +1656,6 @@ class NeonCli(AbstractNeonCli):
 
         return TimelineId(str(created_timeline_id))
 
-    def create_root_branch(
-        self,
-        branch_name: str,
-        tenant_id: Optional[TenantId] = None,
-    ):
-        cmd = [
-            "timeline",
-            "create",
-            "--branch-name",
-            branch_name,
-            "--tenant-id",
-            str(tenant_id or self.env.initial_tenant),
-            "--pg-version",
-            self.env.pg_version,
-        ]
-
-        res = self.raw_cli(cmd)
-        res.check_returncode()
-
-        matches = CREATE_TIMELINE_ID_EXTRACTOR.search(res.stdout)
-
-        created_timeline_id = None
-        if matches is not None:
-            created_timeline_id = matches.group("timeline_id")
-
-        if created_timeline_id is None:
-            raise Exception("could not find timeline id after `neon timeline create` invocation")
-        else:
-            return TimelineId(created_timeline_id)
-
     def create_branch(
         self,
         new_branch_name: str = DEFAULT_BRANCH_NAME,

test_runner/regress/test_neon_local_cli.py

@@ -2,9 +2,16 @@ from fixtures.neon_fixtures import NeonEnvBuilder
 
 
 # Test that neon cli is able to start and stop all processes with the user defaults.
-# def test_neon_cli_basics(neon_simple_env: NeonEnv):
+# Repeats the example from README.md as close as it can
 def test_neon_cli_basics(neon_env_builder: NeonEnvBuilder):
     env = neon_env_builder.init_configs()
+    # Skipping the init step that creates a local tenant in Pytest tests
+    try:
+        env.neon_cli.start()
+        env.neon_cli.create_tenant(tenant_id=env.initial_tenant, set_default=True)
+        env.neon_cli.pg_start(node_name="main")
 
-    env.neon_cli.start()
-    env.neon_cli.stop()
+        env.neon_cli.create_branch(new_branch_name="migration_check")
+        env.neon_cli.pg_start(node_name="migration_check")
+    finally:
+        env.neon_cli.stop()