chore: add kotlin folder

kotlin/spy.kt

@@ -0,0 +1,71 @@
+package spy
+interface Error {
+  var name: String
+  var message: String
+}
+interface CallRecord {
+  var arguments: Array<Any>
+  var result: Any
+  var error: Error
+}
+
+interface Spy {
+  var calls: Array<CallRecord>
+}
+
+/**
+ * Spy on function that uses callback.
+ */
+fun spy<T super Function>(fn: T): T & Spy {
+  const calls: CallRecord[] = []
+  const spiedFn: T = function (...args) {
+    const spiedArgs = args.map(a => {
+      return typeof a === 'function' ? spy(a) : a
+    })
+    const call = { arguments: spiedArgs } as CallRecord
+    calls.push(call)
+    try {
+      const result = fn(...spiedArgs)
+      call.result = result
+      return result
+    }
+    catch (err) {
+      call.error = err
+      throw err
+    }
+  } as any
+
+  return Object.assign(spiedFn, {
+    calls
+  })
+}
+
+
+interface AsyncCallRecord extends Promise<any> {
+  arguments: any[],
+  throws(errback: any): Promise<any>
+}
+
+interface AsyncSpy {
+  calls: ReadonlyArray<AsyncCallRecord>
+}
+
+/**
+ * Spy on function that returns a promise.
+ */
+fun spyAsync<T extends Function>(fn: T): T & AsyncSpy {
+  const calls: AsyncCallRecord[] = []
+  const spiedFn: T = function (...args) {
+    const call = { arguments: args } as AsyncCallRecord
+    calls.push(call)
+    const result = fn(...args)
+    call.then = (cb, eb) => result.then(cb, eb)
+    call.catch = cb => (result.catch(cb))
+    call.throws = call.catch
+    return result
+  } as any
+
+  return Object.assign(spiedFn, {
+    calls
+  })
+}