Test suite, step 1: unit tests for parameters and URLs, tests in CI

[balat]

First step of a test suite for Eliom, which only had two cram tests of the server ppx.

Content

• test/unit: an Alcotest suite for pure functions (no site, no request, no server), run by dune runtest.
  • test_parameter: encoding of typed parameters into HTTP parameters and URL suffixes; decoding back (round trips, typing and wrong-parameter errors, optional values, sets, lists, sums, suffixes and their version without suffix); names used in forms; non-localized parameters. Decoding goes through Parameter_base.reconstruct_params_, since Parameter.reconstruct_params needs a request.
  • test_uri: relative paths, make_actual_path, assembly of URL components, protocol prefixes, and URLs of external services (parameters, suffixes, fragments, preapplied and non-localized parameters).
• Test dependencies: alcotest, and ocsipersist-sqlite because a program linking eliom.server needs an ocsipersist backend.
• CI: pins ocsipersist 3.1.2 (3.1.1 and 3.1.2 fix the lwt and OCaml bounds of ocsipersist-lib) and ocsipersist-sqlite 3.1.2, installs with --with-test, runs dune runtest -p eliom,eliom-compat. The ppx cram tests are attached to the eliom package so that they run with -p.

Each test was checked to fail when the code it covers is broken, by temporarily mutating parameter_base.shared.ml and eliom_uri.shared.ml.

Next steps (separate PRs)

1. Remaining pure unit tests (cookies, wrapping, content, scopes, configuration, registration output), then tests with a site but no request.
2. A harness that runs a test server on a Unix socket, driven by an OCaml client with one cookie jar per simulated browser.
3. State: isolation between sessions, closing sessions, session groups, timeouts.
4. Comet, Bus and React, through a native comet client.
5. Other server features, ppx tests, client tests under node, then end-to-end tests in a browser.