rspec-testing

name

rspec-testing

description

Binxtils' RSpec testing conventions — how to structure specs with `context` and `let`, what kinds of tests to write, and what to avoid (mocks, weakened assertions, testing private methods). Trigger when writing or modifying any `*_spec.rb` file, adding test coverage for new code, refactoring tests, or designing the test layout for a new module. Includes Good/Bad examples of the project's preferred style. (For JavaScript, the Vitest tests live in `index.test.js`.)

RSpec testing in Binxtils

Binxtils is a Ruby gem (the npm package's tests use Vitest in index.test.js). This project uses RSpec; all business logic should be tested. Run the suite with bin/rspec.

Run only the specs your change touches

Pass the files or directories you changed — bin/rspec spec/binxtils/time_parser_spec.rb. A bare bin/rspec runs everything including the type: :system specs, which boot the dummy Rails app. CI runs the full suite.

When something fails outside the files you changed, re-run that spec file on its own before treating it as yours. Passing alone means the full run was order-dependent; failing alone means it's real — and a real failure gets fixed, never excused as pre-existing.

What to test (and what not to)

• Tests should either: help make the code correct now, or prevent bugs in the future. Don't add tests that don't do one of those things.
• Avoid testing private methods (in functionable modules, those are the concealed methods) — test them through the public surface that calls them.
• Avoid mocking objects. Drive the real code path with real inputs.

Stubbing ENV

Never partial-mock ENV with allow(ENV).to receive(:[]).and_call_original — it makes every subsequent ENV[...] lookup go through RSpec's message router, which is slow and easy to break by forgetting a .with(...) branch.

Use stub_const against a merged hash instead:

Good

stub_const("ENV", ENV.to_hash.merge("SECRET_TOKEN" => "test_token"))

Bad

allow(ENV).to receive(:[]).and_call_original
allow(ENV).to receive(:[]).with("SECRET_TOKEN").and_return("test_token")

Always fix failing tests

Fix every failing test, even ones that were already failing on main. Confirming a failure pre-dates your branch (via git stash or checking out main) explains what broke — not whether you fix it. You fix it.

Don't weaken assertions to make a failing test pass

When a test goes red, the correct move is investigate why, not edit the assertion to match the new output. Watch for these tempting "fixes" that are actually erasing signal:

• Changing an expected value to whatever the code now happens to return (e.g. an exact count → a range, a specific string → a substring/regex).
• Loosening eq to include, dropping count: constraints, or replacing expect(...).to ... with expect(...).not_to be_nil.
• Deleting the assertion entirely with a "looks unrelated" handwave.

The right loop: reproduce the failure, figure out what changed and why, then decide intentionally — fix the code if the original assertion captured the right behavior, or update the assertion (with a comment) if the behavior intentionally changed. If you're about to change a test "to make it easier", stop and explain why the new expectation is correct, not just convenient.

Match a target attributes hash, not one attribute at a time

When you're checking several fields on the same object or result, build one expected hash and assert against it in a single matcher. Don't write a chain of one-attribute-per-line expects.

• Object: expect(record).to have_attributes(target_attributes)
• Hash (parsed result, JSON): expect(hash).to eq(target) for a full match, or expect(hash).to include(target_attributes) for partial.

This collapses several brittle assertions into one, makes the contract visible at a glance, and gives a single readable diff when something changes. It also avoids the trap of weak per-field assertions like expect(x).to be_present standing in for "the right value" — match the value directly.

Good

target_attributes = {kind: "found", description: "Some description"}
expect(result).to have_attributes(target_attributes)

Bad

expect(result.kind).to eq("found")
expect(result.description).to be_present
expect(result.description).to eq("Some description")

The bad version spreads one logical assertion across many lines, mixes weak presence checks with the real expected value, and produces noisier failure output.

Structuring with context and let

Use context and let to isolate what varies between examples. Each it block should live in a context that names the condition, with let overrides for only what differs in that case. Avoid repeating setup across sibling it blocks.

Good

RSpec.describe Binxtils::TimeZoneParser, type: :service do
  let(:subject) { described_class }

  describe "parse" do
    let(:target_time_zone) { ActiveSupport::TimeZone[time_zone_str] }

    context "America/Los_Angeles" do
      let(:time_zone_str) { "America/Los_Angeles" }
      it "returns the correct time_zone" do
        expect(subject.parse(time_zone_str)).to eq target_time_zone
        expect(subject.parse(time_zone_str).utc_offset).to eq(-28800)
      end
    end

    context "with an offset prefix" do
      let(:time_zone_str) { "(GMT-07:00) America/Denver" }
      let(:target_time_zone) { ActiveSupport::TimeZone["America/Denver"] }
      it "strips the offset and returns the zone" do
        expect(subject.parse(time_zone_str)).to eq target_time_zone
      end
    end

    context "blank" do
      it "returns nil" do
        expect(subject.parse("")).to be_nil
        expect(subject.parse(nil)).to be_nil
      end
    end
  end
end

Bad

it "returns LA" do
  parser = Binxtils::TimeZoneParser
  expect(parser.parse("America/Los_Angeles")).to eq ActiveSupport::TimeZone["America/Los_Angeles"]
end
it "returns Denver from an offset" do
  parser = Binxtils::TimeZoneParser
  allow(parser).to receive(:something) { true }
  expect(parser.parse("(GMT-07:00) America/Denver")).to eq ActiveSupport::TimeZone["America/Denver"]
end

The bad version repeats setup, mocks the object, and doesn't communicate what each case represents.

One example per distinct setup — combine same-setup it blocks

context/let/before isolate what varies. The corollary runs the other way: if two sibling it blocks share the same setup — no differing context, before, or let override between them — collapse them into one example. Each distinct setup earns exactly one it; put all of that setup's assertions in that single block.

Splitting same-setup assertions across sibling it blocks re-runs identical setup once per block for zero isolation benefit, and scatters one logical behavior across the file. Two it blocks that differ only in the argument passed or the assertion — with identical lets and no before between them — are one example.

After writing a spec, scan each context/describe: if it holds multiple it blocks and they don't each sit behind a distinct context/before/let, merge them.

Good

context "in America/Chicago" do
  let(:time_zone) { ActiveSupport::TimeZone["America/Chicago"] }

  it "parses each supported format" do
    expect(subject.parse("2024-01-15", time_zone)).to eq time_zone.parse("2024-01-15")
    expect(subject.parse("01/15/2024", time_zone)).to eq time_zone.parse("2024-01-15")
    expect(subject.parse("2024-01-15 13:00", time_zone)).to eq time_zone.parse("2024-01-15 13:00")
  end
end

Bad

context "in America/Chicago" do
  let(:time_zone) { ActiveSupport::TimeZone["America/Chicago"] }   # re-built for every it below

  it "parses an ISO date" do
    expect(subject.parse("2024-01-15", time_zone)).to eq time_zone.parse("2024-01-15")
  end
  it "parses a US date" do
    expect(subject.parse("01/15/2024", time_zone)).to eq time_zone.parse("2024-01-15")
  end
  it "parses a datetime" do
    expect(subject.parse("2024-01-15 13:00", time_zone)).to eq time_zone.parse("2024-01-15 13:00")
  end
end

This only merges blocks whose setup is identical. Different setup still means separate examples, each in its own context with the let/before that differs — that's the section above, not a contradiction of it.