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transcriptor

Convert REPL interactions into example-based tests.

Using

transcriptor is in the Maven Central repository.

Clojure deps.edn:

com.cognitect/transcriptor {:mvn/version "0.1.5"}

lein project.clj:

[com.cognitect/transcriptor "0.1.5"]

Problem

Testing frameworks often introduce their own abstractions for e.g. evaluation order, data validation, reporting, scope, code reuse, state, and lifecycle. In my experience, these abstractions are always needlessly different from (and inferior to) related abstractions provided by the language itself.

Adapting an already-working REPL interaction to satisfy such testing abstractions is a waste of time, and it throws away the intermediate REPL results that are valuable in diagnosing a problem.

So transcriptor aims to do less, and impose the bare minimum of cognitive load needed to convert a REPL interaction into a test. The entire API is four functions:

  • xr/run runs a REPL script and produces a transcript
  • check! validates the last returned value against a Clojure spec
  • xr/on-exit lets you register cleanup code to run after xr/run completes
  • xr/repl-files finds the .repl files in a directory tree

Approach

Work at the REPL. Whenever you want to convert a chunk of work into a test, just copy it into a file with a .repl suffix. You can later call xr/run on a REPL file:

(require '[cognitect.transcriptor :as xr :refer (check!)])
(xr/run "your-file-name-here.repl")

run launches a REPL that consumes all forms in the file passed in. run will

  • isolate execution in a one-off namespace whose name is printed to stdout. (If the script fails, you can enter this namespace and poke around.)
  • pretty print every evaluation result, providing a transcript as if you had repeated the REPL interactions by hand.

Evaluation Order

Clojure language (REPL) semantics.

Validation

Clojure language semantics plus one function.

transcriptor includes a single validation form, check!, that will check an argument (by default *1) against a provided spec, throwing an exception if the error does not match:

(+ 1 1)
(check! even?)

Exceptions are failures and unwind the stack back to the call to xr/run.

Reporting

Read clojure.spec error data directly, or pipe it to an error reporter or visualizer of your choice.

Code reuse

Clojure language semantics. Write functions in namespaces and have .repl scripts require them as needed.

Scope

Clojure language semantics. def vars that you need.

State

Clojure language semantics. (For testing code with nontrivial state I recommend simulation-based testing instead).

Lifecycle

Clojure language semantics plus one function.

The xr/on-exit function is a no-op outside xr/run. Inside, it will queue a function that will be called after the REPL exits.

Test Automation

Clojure language semantics plus one function.

  • xr/repl-files returns a seq of .repl files under a directory root, suitable for passing to xr/run.

Test Repeatability

Clojure language semantics.

Keep Dumb Tests Ugly

Tests that want an exact value match can use a Clojure set as a spec:

(+ 1 2)
(check! #{3})  ;; duh

This is ugly by design, as an inducement to test properties instead of specifics.

License

Eclipse Public License, same as Clojure. https://www.eclipse.org/legal/epl-v10.html

Contributing

Please open a Github issue if your have feedback.