fix: Correctly throw error values from method expectations

The following should now throw an error, just like property and function
expectations:

```ts
when(foo.bar()).thenThrow();

instance(foo).bar(); // throws
```

src/expectation/repository/base-repository.ts

@@ -1,3 +1,4 @@
+import { returnOrThrow } from '../../instance/instance';
 import { ApplyProp, Expectation } from '../expectation';
 import { CallMap, ExpectationRepository } from './expectation-repository';
 import { Property } from '../../proxy';
@@ -61,7 +62,7 @@ export abstract class BaseRepository implements ExpectationRepository {
           this.recordExpected(property, args);
           this.countAndConsume(callExpectation);
 
-          return callExpectation.expectation.returnValue.value;
+          return returnOrThrow(callExpectation.expectation.returnValue.value);
         }
 
         this.recordUnexpected(property, args);

src/expectation/repository/repo.contract.ts

@@ -94,6 +94,17 @@ export const repoContractTests: ExpectationRepositoryContract = {
         expect(repo.get('foo')()).toEqual(23);
       },
     },
+    {
+      name: 'should throw if the value is an error',
+      test: (repo) => () => {
+        const expectation = new MatchingCallExpectation('foo', {
+          value: new Error(),
+        });
+        repo.add(expectation);
+
+        expect(() => repo.get('foo')()).toThrow();
+      },
+    },
   ],
 
   'unmet expectations': [

src/instance/instance.ts

@@ -7,7 +7,7 @@ import { createProxy } from '../proxy';
  * Return the expectation's return value. If the value is an error then
  * throw it.
  */
-const returnOrThrow = (returnValue: any) => {
+export const returnOrThrow = (returnValue: any) => {
   if (returnValue instanceof Error) {
     throw returnValue;
   }

tests/e2e.spec.ts

@@ -97,6 +97,17 @@ describe('e2e', () => {
       expect(instance(foo).bar(1)).toEqual(23);
     });
 
+    it('should set expectation on method to throw', () => {
+      interface Foo {
+        bar(x: number): number;
+      }
+
+      const foo = mock<Foo>();
+      when(foo.bar(1)).thenThrow();
+
+      expect(() => instance(foo).bar(1)).toThrow();
+    });
+
     it('should set expectation on member', () => {
       interface Foo {
         bar: number;