YAML Duplicate Keys
Duplicate keys at three nesting levels, including a duplicated top-level sequence. The spec forbids them; most loaders keep the last silently, a few keep the first, and strict linters reject the document. The file publishes the last-wins answer.
# Duplicate keys. YAML 1.2 says a mapping MUST NOT have duplicate keys, but loaders disagree
# about what to do: most keep the LAST occurrence silently, some keep the first, a few raise,
# and strict linters reject the document outright. A config file that quietly loses a setting
# this way is very hard to debug, which is why this fixture exists.
job:
image: registry.example.invalid/ci/runner:1.4
timeout: 10
retries: 1
timeout: 30
image: registry.example.invalid/ci/runner:2.0
stages:
- build
- test
stages:
- deploy
nested:
a:
x: 1
a:
y: 2
expected_last_wins:
job_timeout: 30
job_image: registry.example.invalid/ci/runner:2.0
stages: deploy
nested_a_has_x: false
Specifications
- Duplicated Keys
- 5
- Spec Says
- must not appear
- Common Behaviour
- last wins
- Publishes Expected Last Wins
- true
Testing contract
Expected to recover- Scenario
- Load a mapping containing duplicate keys and record which occurrence the loader keeps
- Expected result
- A last-wins loader yields job.timeout 30 and stages [deploy]; a strict loader rejects the document with a duplicate-key error instead
What is a .yaml file?
YAML (YAML Ain't Markup Language) is a human-readable data-serialization format using indentation, key-value pairs, and lists, and is a superset of JSON. It supports comments, anchors, and multiple documents per file, favoring readability for configuration. Its indentation sensitivity makes it error-prone to hand-edit.
How to use this file
Use an example YAML file to test config parsers, indentation and anchor handling, multi-document streams, and safe-loading to avoid arbitrary object construction.
How to use this file for testing
“YAML Duplicate Keys” is a deterministic Novus Examples fixture for Config parsing, Encoding detection, Editor testing. TOML and INI configuration files with nested sections and typed values — for testing config parsers and loaders.
Documented properties for this file: YAML · 708 bytes. Compare results against paired or grouped companions on this page when present (clean↔damaged, searchable↔scanned, or format twins) so scores stay reproducible across runs.
Download the file once, keep the path stable in CI or local scripts, and treat the spec table as the contract: dimensions, seeds, field lists, and roles are intentional. Corrupt or invalid samples are labelled as such — expect parsers to fail loudly rather than silently accept them.
Pipeline and infrastructure fixtures are inert configuration: steps reference fictional images and scripts, and nothing here executes. Run your linter, schema validator, migrator, or policy engine against them, and expect the deprecated-syntax and intentionally invalid variants to be rejected.
Point your config loader at the file and assert it reads the documented sections and typed values, including any deliberately-tricky nesting or comments.
Code examples
import yaml # pip install pyyaml
with open("duplicate-keys.yaml") as f:
data = yaml.safe_load(f)
print(data)Related files
- yamlYAML Anchors and AliasesAnchors and aliases across mapping, sequence and scalar nodes, including an anchor nested inside another anchored node. The point most tooling misses: an alias is a reference to the same node, so a shallow-loading parser can share mutable state between jobs.
- yamlYAML Block Scalars and Chomping IndicatorsEvery block-scalar variation in one file: literal and folded styles, all three chomping indicators, an explicit indentation indicator, a folded block with a paragraph break, and an embedded shell-shaped script whose own indentation must survive.
- yamlYAML Bounded Anchor ReuseNested anchor reuse kept deliberately small: two anchors, six references, thirty-one expanded nodes. It is here to test alias resolution and expansion accounting on a safe input, and is explicitly not a billion-laughs expansion bomb.
- yamlYAML Directives and CommentsA two-document stream where each document declares its own %YAML directive and the second adds a %TAG handle used by a local tag. Comments appear in every position they are legal, and every one of them is lost by a non-round-tripping loader.
- yamlYAML Explicit and Local TagsExplicit tags across the standard set — !!str, !!float, !!int, !!bool, !!null, !!binary, !!timestamp, !!omap, !!set — alongside two application-local ! tags. CI dialects use local tags in the wild, so a pipeline parser has to decide whether to reject, ignore, or resolve them.
- yamlYAML Flow and Block StylesFlow (JSON-like) and block collections expressing the same structures, nested inside one another in both directions, plus a flow mapping wrapped across lines and a line of strict JSON — which is valid YAML, and a useful check on a parser's JSON-subset claim.
Generated by generation/pipelines.py. Free for any use, no attribution required — license.