2a:null 2b:["$","title",null,{"children":"Test | Tom MacWright | Observable"}] 30:T428,md`# Test

Some folks have been interested in _testing_ their notebooks: here’s an example of using [tape](https://github.com/substack/tape), the little browser-friendly test module to do just that. It requires a little bit of magic to print the test output into a cell as it executes and to color the cell based on test success or failure, but I’ve wrapped that up into a cell that you can import and use pretty easily, or you can just copy-and-paste the relevant code and do your own thing. You can import this notebook to use it in your own like: \`\`\`js import {test} from "@tmcw/test" \`\`\` - Here’s a tiny example of a [notebook that imports and uses test](https://beta.observablehq.com/@tmcw/tests-with-test). - Check out [plenty of good API documentation for the methods under test](https://github.com/substack/tape#methods): you can check equality, state that things are ok, add messages, and so on. Here’s an example of a failing test:`31:[{"id":"dddeba887f05ee3f4eb3106a38bca9630242b8d984fe4bb27a374c61c12dfcedffea5d40c236735445a6cbf80571ec0daaf05e9b46e2b5a3b2b6be54b851acae","href":"https://static.observableusercontent.com/files/dddeba887f05ee3f4eb3106a38bca9630242b8d984fe4bb27a374c61c12dfcedffea5d40c236735445a6cbf80571ec0daaf05e9b46e2b5a3b2b6be54b851acae","name":"tape-4.12.js","type":"application/javascript","lastModified":1578276437612.162,"size":108488}] 2e:{"id":"42bad260749be706","slug":"test","title":"Test","thumbnail":"21a71c19ecf3aae8f775eae2545c70776a7904a05d108ff97e45fe054a831584","access_level":"public","create_time":"$D2018-03-15T17:20:33.393Z","update_time":"$D2020-01-06T02:07:17.612Z","view_time":null,"first_public_time":"$D2018-03-15T18:07:20.318Z","fork":false,"stars":11,"starred":false,"owner":{"type":"team","id":"b47c3705cfcd7c1b","login":"tmcw","name":"Tom MacWright","avatar_url":"https://avatars-next.observableusercontent.com/669bdd774da8a1b9c1b7706ecbc1ea5136b9932c3d5e86b753aa5a098005f674","tier":"starter_2024"},"version":203,"publish_version":203,"role":null,"authored":false,"authors":[{"type":"individual","id":"0bf14b8d9c6eb88a","login":"tmcw","name":"Tom MacWright","avatar_url":"https://avatars-next.observableusercontent.com/669bdd774da8a1b9c1b7706ecbc1ea5136b9932c3d5e86b753aa5a098005f674","tier":null}],"members":[{"type":"individual","id":"0bf14b8d9c6eb88a","login":"tmcw","name":"Tom MacWright","avatar_url":"https://avatars-next.observableusercontent.com/669bdd774da8a1b9c1b7706ecbc1ea5136b9932c3d5e86b753aa5a098005f674","tier":null,"role":"editor"}],"comments":[],"custom_thumbnail":false,"trashed":false,"subscribed":null,"forks":8,"collection":{"id":"7e8c5e7934f7d2f4","slug":"utilities","title":"Utilities","owner":{"id":"b47c3705cfcd7c1b","login":"tmcw","name":"Tom MacWright"}},"type":"notebook","body":{"title":"Test","cells":[{"id":0,"value":"$30","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":35,"value":"test(\"something is wrong\", async t => {\n t.plan(4);\n t.equal(1, 1);\n for (let i = 0; i < 2; i++) {\n t.ok(1, `just making sure everything's okay, part ${i}`);\n await Promises.delay(100);\n }\n t.ok(false, `but this is not ok`);\n})","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":137,"value":"md`And here’s an example of a test that passes:`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":118,"value":"test('making sure that everything is okay', async t => {\n t.plan(4);\n t.equal(1, 1);\n t.inDelta([0.000000000000001, -0.00000000001], [0,0]);\n for (let i = 0; i < 3; i++) {\n t.ok(1, `just making sure everything's okay, part ${i}`);\n await Promises.delay(100);\n }\n})","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":165,"value":"md`The code that makes it work: require tape, and then define a test function that:\n\n- Wraps around tape’s default test function, but tweaks it to:\n- Print the test output into an element, using tape’s createHarness and createStream methods to redirect the stream of output, which usually gets sent to console.log\n- Return a generator that updates every time that there’s test output\n- Makes that output (relatively) pretty\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":91,"value":"test = {\n const tape = await require(await FileAttachment(\"tape-4.12.js\").url());\n tape.Test.prototype.inDelta = inDelta;\n\n return (name, fn, options) => {\n let test = tape.createHarness();\n let stream = test.createStream();\n const output = html`

`\n    const display = html`\n      ${name}
\n      ${output}\n    `\n    test(name, fn, options);\n    return Generators.observe(change => {\n      let results = '';\n      let failed = false;\n      stream.on('data', d => {\n        output.appendChild(document.createTextNode(d));\n        if (d.startsWith('not ok')) {\n          display.firstChild.style.background = '#FFDFDF';\n          failed = true;\n        }\n        change(display);\n      });\n    });\n  }\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":201,"value":"inDelta = {\n  function inDelta(actual, expected, delta) {\n    return (Array.isArray(expected) ? inDeltaArray : inDeltaNumber)(\n      actual,\n      expected,\n      delta\n    );\n  }\n  function inDeltaArray(actual, expected, delta) {\n    var n = expected.length,\n      i = -1;\n    if (actual.length !== n) return false;\n    while (++i < n) if (!inDelta(actual[i], expected[i], delta)) return false;\n    return true;\n  }\n  function inDeltaNumber(actual, expected, delta) {\n    return actual >= expected - delta && actual <= expected + delta;\n  }\n  return function(actual, expected, delta) {\n    delta = delta || 1e-6;\n    this._assert(inDelta(actual, expected, delta), {\n      message: \"should be in delta \" + delta,\n      operator: \"inDelta\",\n      actual: actual,\n      expected: expected\n    });\n  };\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"}],"files":"$W31","stdlib":"1","titling":"auto"}}
2f:"$2e:body"