Mock VLM provider for testing

Mock VLM provider for testing

Mock VLM provider for testing

Details

A stand-in for an ellmer chat object. Exposes the same $chat(prompt, ...) method, but instead of calling a model it pops the next response from a pre-loaded queue. Designed for testthat unit tests that exercise extraction logic without API keys or network access.

Each call to $chat() returns the next element of the responses list. If the call number matches validation_error_at, that response is replaced with a deliberately malformed JSON string, allowing tests to exercise the retry-on-validation-failure path implemented in validate_or_retry.

Example

good_json <- '{"horizons": [...]}'
mock <- MockVLMProvider$new(responses = list(good_json))
result <- mock$chat("any prompt")  # returns good_json

# Simulate one validation error before success.
mock <- MockVLMProvider$new(
  responses = list("not really json", good_json),
  validation_error_at = NULL  # already invalid as-is
)

# Or force an attempt to be invalid via the helper.
mock <- MockVLMProvider$new(
  responses = list(good_json, good_json),
  validation_error_at = 1L
)

Inspection

After use, the mock exposes $call_count (integer) and $prompts_received (list of every prompt passed to $chat()), which lets tests assert that retry prompts include the previous validation error.

Public fields

responses

List of canned responses (character scalars or R objects to be JSON-serialised).

validation_error_at

Optional integer; when the call number matches, the returned text is replaced with a malformed JSON string.

call_count

Integer counter (0 before any call).

prompts_received

List recording every prompt passed to $chat().

Methods

Public methods

• MockVLMProvider$new()

• MockVLMProvider$chat()

• MockVLMProvider$reset()

• MockVLMProvider$clone()

---

Method new()

Construct a mock provider.

Usage

MockVLMProvider$new(responses = list(), validation_error_at = NULL)

Arguments

responses

List of canned responses. Strings are returned verbatim; non-string elements are JSON-serialised via jsonlite::toJSON.

validation_error_at

Optional integer giving the 1-based index of an attempt that should return malformed JSON (to test the retry path). Use NULL (default) to always return the queued response unchanged.

---

Method chat()

Send a prompt; returns the next queued response.

Usage

MockVLMProvider$chat(prompt, ...)

Arguments

prompt

Character scalar (the rendered prompt). Stored in $prompts_received.

...

Additional arguments are accepted (and ignored) so the signature matches multimodal calls that pass an image content object after the prompt.

Returns

Character scalar with the response text.

---

Method reset()

Reset the mock (call count and prompt log).

Usage

MockVLMProvider$reset()

---

Method clone()

The objects of this class are cloneable with this method.

Usage

MockVLMProvider$clone(deep = FALSE)

Arguments

deep

Whether to make a deep clone.