Reimplement t.throws() and t.notThrows() (#1704)

Remove `core-assert` dependency. When passed a function as the second
argument, `t.throws()` now assumes its a constructor. This removes
support for a validation function, which may or may not have worked.
Refs #1047.

`t.throws()` now fails if the exception is not an error. Fixes #1440.

Regular expressions are now matched against the error message, not the
result of casting the error to a string. Fixes #1445.

Validate second argument to `t.throws()`. Refs #1676.

Assertion failures now display how AVA arrived at the exception.
Constructors are printed when the error is not a correct instance.
Fixes #1471.

Support expectation object in t.throws()

Fixes #1047. Fixes #1676.

A combination of the following expectations is supported:

```js
t.throws(fn, {instanceOf: SyntaxError}) // err instanceof SyntaxError
t.throws(fn, {name: 'SyntaxError'}) // err.name === 'SyntaxError'
t.throws(fn, {is: expectedErrorInstance}) // err === expectedErrorInstance
t.throws(fn, {message: 'expected error message'}) // err.message === 'expected error message'
t.throws(fn, {message: /expected error message/}) // /expected error message/.test(err.message)
```

index.d.ts

@@ -2,7 +2,16 @@ export interface ObservableLike {
 	subscribe(observer: (value: any) => void): void;
 }
 
-export type ThrowsErrorValidator = (new (...args: Array<any>) => any) | RegExp | string | ((error: any) => boolean);
+export type Constructor = (new (...args: Array<any>) => any);
+
+export type ThrowsExpectation = {
+	instanceOf?: Constructor;
+	is?: Error;
+	message?: string | RegExp;
+	name?: string;
+};
+
+export type ThrowsErrorValidator = Constructor | RegExp | string | ThrowsExpectation;
 
 export interface SnapshotOptions {
 	id?: string;

index.js.flow

@@ -7,7 +7,16 @@ export interface ObservableLike {
 	subscribe(observer: (value: any) => void): void;
 }
 
-export type ThrowsErrorValidator = Class<{constructor(...args: Array<any>): any}> | RegExp | string | ((error: any) => boolean);
+export type Constructor = Class<{constructor(...args: Array<any>): any}>;
+
+export type ThrowsExpectation = {
+	instanceOf?: Constructor;
+	is?: Error;
+	message?: string | RegExp;
+	name?: string;
+};
+
+export type ThrowsErrorValidator = Constructor | RegExp | string | ThrowsExpectation;
 
 export interface SnapshotOptions {
 	id?: string;