fix issue in pow and better coverage

Author: make-github-pseudonymous-again

src/Integer.js

@@ -162,7 +162,7 @@ export class Integer {
 	 */
 	pow ( x ) {
 
-		const is_negative = Math.pow( this.is_negative , x ) ;
+		const is_negative = this.is_negative & x & 1 ? -1 : 0 ;
 
 		const a = this.limbs ;
 		const c = _zeros( Math.max( 1 , a.length * x ) ) ;

src/IntegerRing.js

@@ -62,7 +62,7 @@ export class IntegerRing {
 
 	from_string ( string , base = 10 , is_negative = 0  ) {
 
-		if ( string.length === 0 ) throw 'IntegerRing#from_string cannot parse empty string.' ;
+		if ( string.length === 0 ) throw new ValueError( 'IntegerRing#from_string cannot parse empty string.' ) ;
 
 		if ( string[0] === '-' ) return this.from_string( string.slice(1) , base , ~is_negative ) ;
 

test/src/ZZ/from.js

@@ -13,11 +13,19 @@ test( 'ZZ.from()' , t => {
 	t.is( ZZ.from(false).toString() , '0' ) ;
 	t.is( ZZ.from(1===0).toString() , '0' ) ;
 	t.is( ZZ.from('+10').toString() , '10' ) ;
+	t.is( ZZ.from(ZZ.from(2, undefined, -1).pow(12)).toString(), '4096')
+	t.is( ZZ.from(ZZ.from(2, undefined, 0).pow(12)).toString(), '4096')
+	t.is( ZZ.from(ZZ.from(2, undefined, -1).pow(11)).toString(), '-2048')
+	t.is( ZZ.from(ZZ.from(2, undefined, 0).pow(11)).toString(), '2048')
 
 	t.throws( () => ZZ.from({}) , TypeError ) ;
 	t.throws( () => ZZ.from(new Date()) , TypeError ) ;
 	t.throws( () => ZZ.from(new Regex()) , TypeError ) ;
 
+	t.throws( () => ZZ.from('') , ValueError ) ;
+	t.throws( () => ZZ.from('-') , ValueError ) ;
+	t.throws( () => ZZ.from('+') , ValueError ) ;
+	t.throws( () => ZZ.from('+---+-+') , ValueError ) ;
 	t.throws( () => ZZ.from(1, 2) , ValueError ) ;
 	t.throws( () => ZZ.from(true, 2) , ValueError ) ;
 	t.throws( () => ZZ.from(ZZ.from(17), 2) , ValueError ) ;