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Using the ctx · 58 / 69

Simulate a cache with a function fake

YOUR TASK

Make this happen

3 steps

  1. Return the fallback for a miss or failed call, and keep valid cached values. The spy checks how often the host was called and which key it received. Each test case has fresh mocks and call history.

  2. Read the cases in lesson.test.lua, then choose Check solution to see what needs to change.

  3. Update subject.lua until every test passes. Keep the supplied tests unchanged.

Start with Check solution, then use the failures to guide your edits.

Read the starter and tests

subject.lua

exports.lookup = function(key: string, fallback: string)
  local ok, value = ctx.cache.get(key)
  return value
end

lesson.test.lua

local t = require("test")
local subject = require("cococo.subject")

t.it("returns values by key and handles a miss", function()
  t.mock.host("ctx.cache.get"):using(function(key)
    if key == "job:42" then
      return true, "ready"
    end
    return true, nil
  end)
  local s = subject.load()
  t.expect(s.lookup("job:42", "unknown")):eq("ready")
  t.expect(s.lookup("job:99", "unknown")):eq("unknown")
  t.expect(t.mock.spy("ctx.cache.get")):called_times(2)
  t.expect(t.mock.spy("ctx.cache.get")):called_with("job:99")
end)
t.it("handles a failed cache call", function()
  t.mock.host("ctx.cache.get"):returns(false, "offline")
  local s = subject.load()
  t.expect(s.lookup("job:42", "unknown")):eq("unknown")
end)