assert: Add equalWithMargin for floating and other number comparison with error margin

README.md

@@ -111,9 +111,11 @@ $ eltro --watch my_watch_name --npm build
 
 Not only does eltro allow you to use any assertion library of your own choosing, it also comes with it's own assertion library based on node's default [assert](https://nodejs.org/api/assert.html) with a few extra methods:
 
+ * `assert.equalWithMargin(value, test, margin, [message])`: Check if number value is equal to test with error margin.
  * `assert.notOk(value, [message])`: Assert value is not ok.
  * `assert.match(value, test, [message])`: Check if value matches RegExp test.
  * `assert.notMatch(value, [message])`: Check if value does not match RegExp test.
+ * `assert.throwsAndCatch(fn, [message])`: Checks if function fn throws and returns the thrown error.
  * `assert.isFulfilled(promise, [message])`: Assert the promise resolves.
  * `assert.isRejected(promise, [message])`: Assert the promise gets rejects.
 

lib/assert.mjs

@@ -57,6 +57,14 @@ assert.throwsAndCatch = (fn, message) => {
   return err
 }
 
+assert.equalWithMargin = (value, test, margin = 0.005, message) => {
+  assert.strictEqual(typeof value, 'number', 'Value should be number')
+  assert.strictEqual(typeof test, 'number', 'Test should be number')
+
+  let difference = Math.abs(value - test)
+  assert.ok(difference <= margin, message || `${value} ± ${margin} != ${test} (difference of ${difference} > ${margin})`)
+}
+
 assert.isFulfilled = (promise, message) => {
   return Promise.resolve(true)
     .then(() => promise)

package.json

@@ -1,6 +1,6 @@
 {
   "name": "eltro",
-  "version": "1.4.6",
+  "version": "1.5.0",
   "description": "Eltro is a tiny no-dependancy test framework for node",
   "main": "index.mjs",
   "scripts": {

test/assert.test.mjs

@@ -29,6 +29,41 @@ t.describe('#notOk()', function() {
   })
 })
 
+t.describe('#equalWithMargin()', function() {
+  t.test('should support default margin for floating point math', function() {
+    let check = 0.1 + 0.2
+
+    assertExtended.throws(function() {
+      assertExtended.strictEqual(check, 0.3)
+    }, assertExtended.AssertionError)
+
+    assertExtended.equalWithMargin(check, 0.3)
+  })
+
+  t.test('should support custom margin', function() {
+    assertExtended.equalWithMargin(1, 2, 1)
+  })
+
+  t.test('should fail if margin is too small', function() {
+    assertExtended.throws(function() {
+      assertExtended.equalWithMargin(1, 2, 0.9)
+    }, assertExtended.AssertionError)
+  })
+
+  t.test('should support custom message', function () {
+    const assertMessage = 'Hello world'
+    let error = null
+
+    try {
+      assertExtended.equalWithMargin(1, 2, 0, assertMessage)
+    } catch (err) {
+      error = err
+    }
+    assert.ok(error)
+    assert.match(error.message, new RegExp(assertMessage))
+  })
+})
+
 t.describe('#throwAndCatch()', function() {
   t.test('should work and return the original error', function() {
     const assertError = new Error('Speed')