Add regression test

Author: ahejlsberg

testdata/baselines/reference/compiler/expandoFunctionAsAssertion.symbols

@@ -0,0 +1,27 @@
+//// [tests/cases/compiler/expandoFunctionAsAssertion.ts] ////
+
+=== expandoFunctionAsAssertion.ts ===
+function example() {}
+>example : Symbol(example, Decl(expandoFunctionAsAssertion.ts, 0, 0))
+
+example.isFoo = function isFoo(value: string): asserts value is 'foo' {
+>example.isFoo : Symbol(example.isFoo, Decl(expandoFunctionAsAssertion.ts, 0, 21))
+>example : Symbol(example, Decl(expandoFunctionAsAssertion.ts, 0, 0))
+>isFoo : Symbol(example.isFoo, Decl(expandoFunctionAsAssertion.ts, 0, 21))
+>isFoo : Symbol(isFoo, Decl(expandoFunctionAsAssertion.ts, 2, 15))
+>value : Symbol(value, Decl(expandoFunctionAsAssertion.ts, 2, 31))
+>value : Symbol(value, Decl(expandoFunctionAsAssertion.ts, 2, 31))
+
+  if (value !== 'foo') {
+>value : Symbol(value, Decl(expandoFunctionAsAssertion.ts, 2, 31))
+
+    throw new Error('Not foo');
+>Error : Symbol(Error, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+  }
+};
+
+example.isFoo('test');
+>example.isFoo : Symbol(example.isFoo, Decl(expandoFunctionAsAssertion.ts, 0, 21))
+>example : Symbol(example, Decl(expandoFunctionAsAssertion.ts, 0, 0))
+>isFoo : Symbol(example.isFoo, Decl(expandoFunctionAsAssertion.ts, 0, 21))
+

testdata/baselines/reference/compiler/expandoFunctionAsAssertion.types

@@ -0,0 +1,34 @@
+//// [tests/cases/compiler/expandoFunctionAsAssertion.ts] ////
+
+=== expandoFunctionAsAssertion.ts ===
+function example() {}
+>example : { (): void; isFoo: (value: string) => asserts value is "foo"; }
+
+example.isFoo = function isFoo(value: string): asserts value is 'foo' {
+>example.isFoo = function isFoo(value: string): asserts value is 'foo' {  if (value !== 'foo') {    throw new Error('Not foo');  }} : (value: string) => asserts value is "foo"
+>example.isFoo : (value: string) => asserts value is "foo"
+>example : { (): void; isFoo: (value: string) => asserts value is "foo"; }
+>isFoo : (value: string) => asserts value is "foo"
+>function isFoo(value: string): asserts value is 'foo' {  if (value !== 'foo') {    throw new Error('Not foo');  }} : (value: string) => asserts value is "foo"
+>isFoo : (value: string) => asserts value is "foo"
+>value : string
+
+  if (value !== 'foo') {
+>value !== 'foo' : boolean
+>value : string
+>'foo' : "foo"
+
+    throw new Error('Not foo');
+>new Error('Not foo') : Error
+>Error : ErrorConstructor
+>'Not foo' : "Not foo"
+  }
+};
+
+example.isFoo('test');
+>example.isFoo('test') : void
+>example.isFoo : (value: string) => asserts value is "foo"
+>example : { (): void; isFoo: (value: string) => asserts value is "foo"; }
+>isFoo : (value: string) => asserts value is "foo"
+>'test' : "test"
+

testdata/tests/cases/compiler/expandoFunctionAsAssertion.ts

@@ -0,0 +1,12 @@
+// @strict: true
+// @noEmit: true
+
+function example() {}
+
+example.isFoo = function isFoo(value: string): asserts value is 'foo' {
+  if (value !== 'foo') {
+    throw new Error('Not foo');
+  }
+};
+
+example.isFoo('test');