move backoff into codebase

test/backoff-test.ts

@@ -0,0 +1,37 @@
+import assert from 'assert-diff'
+import {ExponentialBackoff} from '../src/common/backoff'
+
+describe('ExponentialBackoff', function() {
+  it('duration() return value starts with the min value', function() {
+    // default: 100ms
+    assert(new ExponentialBackoff().duration(), 100)
+    assert(new ExponentialBackoff({min: 100}).duration(), 100)
+    assert(new ExponentialBackoff({min: 123}).duration(), 123)
+  })
+
+  it('duration() return value increases when called multiple times', function() {
+    const backoff = new ExponentialBackoff({min: 100, max: 1000})
+    assert.strictEqual(backoff.duration(), 100)
+    assert.strictEqual(backoff.duration(), 200)
+    assert.strictEqual(backoff.duration(), 400)
+    assert.strictEqual(backoff.duration(), 800)
+  })
+
+  it('duration() never returns greater than the max value', function() {
+    const backoff = new ExponentialBackoff({min: 300, max: 1000})
+    assert.strictEqual(backoff.duration(), 300)
+    assert.strictEqual(backoff.duration(), 600)
+    assert.strictEqual(backoff.duration(), 1000)
+    assert.strictEqual(backoff.duration(), 1000)
+  })
+
+  it('reset() will reset the duration() value', function() {
+    const backoff = new ExponentialBackoff({min: 100, max: 1000})
+    assert.strictEqual(backoff.duration(), 100)
+    assert.strictEqual(backoff.duration(), 200)
+    assert.strictEqual(backoff.duration(), 400)
+    backoff.reset()
+    assert.strictEqual(backoff.duration(), 100)
+    assert.strictEqual(backoff.duration(), 200)
+  })
+})