Description
Construct caller srcset candidates with unique sampled descriptors and controlled mixed/duplicate/zero mutations, retaining actual lexical parser outcomes without selecting a browser image source.
A protocol fixture is local test data representing headers, messages, identifiers, or request decisions. Serialization and parsing can be checked without contacting a server, while authentication, delivery, and actual client behavior require separate tests.
Construct caller srcset candidates with unique sampled descriptors and controlled mixed/duplicate/zero mutations, retaining actual lexical parser outcomes without selecting a browser image source.
When to use this tool
Use this generator to create reproducible responsive image source fixture cases from the supplied model or bank. Inspect the returned evidence before using cases in a test or exercise.
How to use the tool and how it works
- Supply candidates, kind, candidatesPerCase, modes, count in the field shapes below. Set seed when you need an explicit replay.
- Run the tool and correct any input error. For generated controls, distinguish a successful fixture containing an invalid case from failure to generate the fixture.
- Read cases. Use the conventions below and keep answer-bearing fields separate when presenting an exercise.
Select distinct responsive-image candidates and serialize width or density descriptors. Apply valid, zero, duplicate, or mixed-descriptor modes, then retain either the delegated srcset parse or the expected parser issue and verify the intended outcome.1
Delegated operations used for this result: srcset parser. Their calculation or parsing conventions apply to the corresponding result fields.2
| Input field | Meaning and units | Accepted input |
|---|---|---|
| candidates | Candidates | Required. Array of Object; no unknown keys.; minimum items 1; maximum items 16. |
| candidates[].url | Url | Required. Text; minimum UTF-16 length 1; maximum UTF-16 length 128. |
| candidates[].value | Value | Required. Finite number; strictly above 0. |
| kind | Kind | Required. Text; one of "width", "density". |
| candidatesPerCase | Candidates Per Case | Required. Safe integer; minimum 1; maximum 16. |
| modes | Modes | Required. Array of Text; one of "valid", "duplicate", "zero", "mixed".; minimum items 1; maximum items 4. |
| count | Requested count; the mechanics explain whether one draw expands into several returned records. | Required. Safe integer; minimum 1; maximum 32. |
| seed | Optional numeric seed; takes precedence over context randomness. Without either, use the fixed tool.io default seed. | Optional. Safe integer. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| cases | Cases | Required. Array of Object; no unknown keys.; minimum items 1; maximum items 32. |
| cases[].mode | Mode | Required. Text; one of "valid", "duplicate", "zero", "mixed". |
| cases[].srcset | Srcset | Required. Text; maximum UTF-16 length 131072. |
| cases[].parserResult | Parser Result | Required. Object; no unknown keys. or Null. |
| cases[].parserError | Parser Error | Required. Object; no unknown keys. or Null. |
| randomness | Replay metadata: source is seed or context; seed is the normalized 32-bit seed or null for a context source. | Required. Object; no unknown keys. |
| randomness.seed | Optional numeric replay seed; normalization and precedence are explained below. | Required. Safe integer. or Null. |
| randomness.source | Source | Required. Text; one of "context", "seed". |
An explicit safe-integer seed takes precedence over injected context randomness and is normalized to an unsigned 32-bit integer. With no seed and no context source, replay uses the fixed tool.io default seed. A context source must return finite values from zero inclusive to one exclusive; its advancing state must be retained separately. randomness records the source and normalized seed, or null for context. These generators are not cryptographic random sources.
{
"input": {
"candidates": [
{
"url": "a.png",
"value": 100
},
{
"url": "b.png",
"value": 200
}
],
"kind": "width",
"candidatesPerCase": 2,
"modes": [
"valid",
"duplicate",
"zero",
"mixed"
],
"count": 1,
"seed": 42
},
"output": {
"cases": [
{
"mode": "mixed",
"srcset": "b.png 200w, a.png 2x",
"parserResult": null,
"parserError": {
"field": "srcset",
"code": "mixed_descriptors"
}
}
],
"randomness": {
"seed": 42,
"source": "seed"
}
}
}Limitations and assumptions
- Width descriptors require integers. Duplicate and mixed controls require at least two candidates. This checks syntax rather than downloading images, evaluating sizes, or choosing a browser resource.
- A replay requires the same complete input and implementation. Randomized construction does not guarantee uniform coverage of every feasible output; finite samples can repeat unless a distinct-selection rule is explicitly stated.
- The field tables state structural bounds; cross-field constraints and bounded search or output budgets also apply. Unknown keys are rejected where the object contract disallows them. Input errors are distinct from null fields and deliberate invalid controls in a successful output.
Alternative or Complementary methods
For a supplied example, inspect the returned construction or delegated check directly. To evaluate a consumer, also test cases chosen for its own boundaries; a generated finite corpus does not establish exhaustive coverage.
References
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