ReqCassette.
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Formats debugging information for template matching failures and provides optional logging during template extraction and matching.
When a template match fails during replay, this module provides detailed diff output to help developers understand what went wrong and how to fix it.
Debug Logging
Enable debug logging by setting debug: true in template options:
template: [preset: :anthropic, debug: true]This will log:
- Pattern extraction results during recording
- Template match attempts during replay
Example Output
Template match failed for cassette "sku_lookup"
Expected template structure:
Method: GET
URI: https://api.example.com/sku/{{sku.0}}
Body: List SKU {{sku.0}} separated from SKU {{sku.1}}
Incoming request (templated):
Method: GET
URI: https://api.example.com/sku/{{sku.0}}
Body: List SKU {{sku.0}} but exclude SKU {{sku.1}}
^^^^^^^^^^^
Difference detected here
Extracted variables:
sku.0 = "6785-9443"
sku.1 = "3488-3234"
Hint: The request structure changed. Update cassette or adjust patterns.Summary
Functions
Formats a detailed diff for a template match failure.
Formats a request summary for display.
Formats extracted variables for display.
Logs pattern extraction results during recording.
Logs a template match attempt during replay.
Functions
Formats a detailed diff for a template match failure.
Parameters
cassette_request- The templated request from the cassetteincoming_request- The templated incoming requestdiff- The diff information from the matcher (what field differs)variables- The extracted variables from the incoming request
Returns
A formatted string with the diff information
Examples
iex> cassette_req = %{
...> "method" => "GET",
...> "uri" => "https://api.example.com/sku/{{sku.0}}",
...> "body" => "Get {{sku.0}}"
...> }
iex> incoming_req = %{
...> "method" => "POST",
...> "uri" => "https://api.example.com/sku/{{sku.0}}",
...> "body" => "Get {{sku.0}}"
...> }
iex> diff = %{field: "method", expected: "GET", actual: "POST"}
iex> variables = %{sku: ["1234"]}
iex> message = format_diff(cassette_req, incoming_req, diff, variables)
iex> String.contains?(message, "Method mismatch")
trueFormats a request summary for display.
This is a public helper that can be reused by other modules (e.g., Mix tasks for cassette inspection).
Parameters
request- A request map with method, uri, query_string, and body fields
Returns
A formatted string summarizing the request.
Formats extracted variables for display.
This is a public helper that can be reused by other modules (e.g., Mix tasks for cassette inspection).
Parameters
variables- Map of variable names to lists of values
Returns
A formatted string showing each variable and its values.
Examples
iex> format_variables(%{sku: ["1234", "5678"], order_id: ["ORD-1"]})
" sku.0 = \"1234\"\n sku.1 = \"5678\"\n order_id.0 = \"ORD-1\""Logs pattern extraction results during recording.
When enabled is true, logs the patterns used and variables extracted.
When enabled is false, this is a no-op.
Parameters
variables- Map of extracted variables (e.g.,%{sku: ["1234-5678"]})patterns- Map of pattern names to regexesenabled- Whether debug logging is enabled
Examples
iex> log_extraction(%{sku: ["1234"]}, %{sku: ~r/\d{4}/}, true)
:okLogs a template match attempt during replay.
When enabled is true, logs whether the match succeeded or failed,
with detailed diff information on failure.
When enabled is false, this is a no-op.
Parameters
cassette_request- The templated request from the cassetteincoming_request- The templated incoming requestresult- Either:matchor{:error, diff}variables- The extracted variables from the incoming requestenabled- Whether debug logging is enabled
Examples
iex> log_match_attempt(%{...}, %{...}, :match, %{sku: ["1234"]}, true)
:ok