tests

Author: Harris-Miller

test/propEq.test.ts

@@ -3,85 +3,86 @@ import { expectError, expectType } from 'tsd';
 import { propEq } from '../es';
 
 type Obj = {
-  union: 'foo' | 'bar';
-  str: string;
-  num: number;
-  u: undefined;
-  n: null;
+  literals: 'A' | 'B';
+  union: number | string;
+  nullable: number | null;
+  optional?: number;
 };
 
-const str: string = '';
-// explanation
-
-// `string` is too wide for `'foo' | 'bar` for assignment
-({} as Obj).union = str;
-// but for comparison is fine
-({} as Obj).union === str;
-// null and undefined are allowed as well
-({} as Obj).str === null;
-({} as Obj).str === undefined;
-
-// this is why we use `WidenLiterals` in the type definition
-
-// propEq(val, name, obj)
-expectType<boolean>(propEq('foo', 'union', {} as Obj));
-// any string works here, see the above explanation as to why
-expectType<boolean>(propEq('else', 'union', {} as Obj));
-// also null or undefined
-expectType<boolean>(propEq(null, 'union', {} as Obj));
-expectType<boolean>(propEq(undefined, 'union', {} as Obj));
-// completely different type fails
-expectError(propEq(2, 'union', {} as Obj));
-// other props work as expected
-expectType<boolean>(propEq(2, 'num', {} as Obj));
-expectError(propEq(2, 'u', {} as Obj));
-expectType<boolean>(propEq(2, 'num', {} as Obj));
-expectError(propEq(2, 'n', {} as Obj));
-expectType<boolean>(propEq(null, 'n', {} as Obj));
-expectError(propEq(2, 'n', {} as Obj));
-expectType<boolean>(propEq(undefined, 'u', {} as Obj));
+const obj = {} as Obj;
 
 // propEq(val)(name)(obj)
-expectType<boolean>(propEq('foo')('union')({} as Obj));
-// any string works here, see the above explanation as to why
-expectType<boolean>(propEq('else')('union')({} as Obj));
-// completely different type fails
-expectError(propEq(2, 'union', {} as Obj));
-// other props work as expected
-expectType<boolean>(propEq(2, 'num', {} as Obj));
-expectError(propEq(2)('u')({} as Obj));
-expectType<boolean>(propEq(2)('num')({} as Obj));
-expectError(propEq(2)('n')({} as Obj));
-expectType<boolean>(propEq(null, 'n', {} as Obj));
-expectError(propEq(2)('n')({} as Obj));
-expectType<boolean>(propEq(undefined, 'u', {} as Obj));
+expectType<boolean>(propEq('A')('literals')(obj));
+// any string works here and will return boolean, we can live with that
+expectType<boolean>(propEq('C')('literals')(obj));
+// a different base type returns `never`
+expectType<never>(propEq(2)('literals')(obj));
+// unions work
+expectType<boolean>(propEq(2)('union')(obj));
+expectType<boolean>(propEq('2')('union')(obj));
+expectType<never>(propEq(true)('union')(obj));
+// nullable works
+expectType<boolean>(propEq(2)('nullable')(obj));
+expectType<boolean>(propEq(null)('nullable')(obj));
+// optionals work
+expectType<boolean>(propEq(2)('optional')(obj));
+expectType<boolean>(propEq(undefined)('optional')(obj));
+// unknownKey errors
+expectError(propEq('whatever')('unknownKey')(obj));
 
 // propEq(val)(name, obj)
-expectType<boolean>(propEq('foo')('union', {} as Obj));
-// 'nope' is inferred as 'string' here.
-expectType<boolean>(propEq('nope')('union', {} as Obj));
-// completely different type fails
-expectError(propEq(2)('union', {} as Obj));
-// other props work as expected
-expectType<boolean>(propEq(2)('num', {} as Obj));
-expectError(propEq(2)('u', {} as Obj));
-expectType<boolean>(propEq(2)('num', {} as Obj));
-expectError(propEq(2)('n', {} as Obj));
-expectType<boolean>(propEq(null)('n', {} as Obj));
-expectError(propEq(2)('n', {} as Obj));
-expectType<boolean>(propEq(undefined, 'u', {} as Obj));
+expectType<boolean>(propEq('A')('literals', obj));
+// any string works here and will return boolean, we can live with that
+expectType<boolean>(propEq('C')('literals', obj));
+// a different base type returns `never`
+expectType<never>(propEq(2)('literals', obj));
+// unions work
+expectType<boolean>(propEq(2)('union', obj));
+expectType<boolean>(propEq('2')('union', obj));
+expectType<never>(propEq(true)('union', obj));
+// nullable works
+expectType<boolean>(propEq(2)('nullable', obj));
+expectType<boolean>(propEq(null)('nullable', obj));
+// optionals work
+expectType<boolean>(propEq(2)('optional', obj));
+expectType<boolean>(propEq(undefined)('optional', obj));
+// unknownKey errors
+expectError(propEq('whatever')('unknownKey', obj));
 
 // propEq(val, name)(obj)
-expectType<boolean>(propEq('foo', 'union')({} as Obj));
-// any string works here, see the above explanation as to why
-expectType<boolean>(propEq('else', 'union')({} as Obj));
-// completely different type fails
-expectError(propEq(2, 'union')({} as Obj));
-// other props work as expected
-expectType<boolean>(propEq(2, 'num')({} as Obj));
-expectError(propEq(2, 'u')({} as Obj));
-expectType<boolean>(propEq(2, 'num')({} as Obj));
-expectError(propEq(2, 'n')({} as Obj));
-expectType<boolean>(propEq(null, 'n')({} as Obj));
-expectError(propEq(2, 'n')({} as Obj));
-expectType<boolean>(propEq(undefined, 'u')({} as Obj));
+expectType<boolean>(propEq('A', 'literals')(obj));
+// any string works here and will return boolean, we can live with that
+expectType<boolean>(propEq('C', 'literals')(obj));
+// a different base type returns `never`
+expectType<never>(propEq(2, 'literals')(obj));
+// unions work
+expectType<boolean>(propEq(2, 'union')(obj));
+expectType<boolean>(propEq('2', 'union')(obj));
+expectType<never>(propEq(true, 'union')(obj));
+// nullable works
+expectType<boolean>(propEq(2, 'nullable')(obj));
+expectType<boolean>(propEq(null, 'nullable')(obj));
+// optionals work
+expectType<boolean>(propEq(2, 'optional')(obj));
+expectType<boolean>(propEq(undefined, 'optional')(obj));
+// unknownKey errors
+expectError(propEq('whatever', 'unknownKey')(obj));
+
+// propEq(val, name, obj)
+expectType<boolean>(propEq('A', 'literals', obj));
+// any string works here and will return boolean, we can live with that
+expectError(propEq('C', 'literals', obj));
+// a different base type returns `never`
+expectError(propEq(2, 'literals', obj));
+// unions work
+expectType<boolean>(propEq(2, 'union', obj));
+expectType<boolean>(propEq('2', 'union', obj));
+expectError(propEq(true, 'union', obj));
+// nullable works
+expectType<boolean>(propEq(2, 'nullable', obj));
+expectType<boolean>(propEq(null, 'nullable', obj));
+// optionals work
+expectType<boolean>(propEq(2, 'optional', obj));
+expectType<boolean>(propEq(undefined, 'optional', obj));
+// unknownKey errors
+expectError(propEq('whatever', 'unknownKey', obj));