refactor: update tests to handle nonnegative weights

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Author: anandkaranubc

lib/node_modules/@stdlib/stats/incr/wstdev/lib/main.js

@@ -88,7 +88,7 @@ var format = require( '@stdlib/string/format' );
 *     \sigma_n = \sqrt{\frac{M2_n}{W_n}}
 *     ```
 *
-* -   Incrementally updating the weighted mean:
+* -   Incrementally updating the weighted sample mean:
 *
 *     ```tex
 *     \begin{align*}
@@ -160,7 +160,7 @@ function incrwstdev( mean ) {
 			throw new TypeError( format( 'invalid argument. Second argument must be a nonnegative number. Value: `%s`.', w ) );
 		}
 		if ( w === 0.0 ) {
-			return ( FLG === void 0 ) ? null : mu;
+			return ( FLG === void 0 ) ? null : sqrt( M2 / wsum );
 		}
 		FLG = true;
 		delta = x - mu;

lib/node_modules/@stdlib/stats/incr/wstdev/test/test.js

@@ -72,22 +72,46 @@ tape( 'the function throws an error if provided a non-numeric value', function t
 	}
 });
 
-tape( 'the weighted sample standard deviation is `null` until at least 1 datum has been provided (known mean)', function test( t ) {
-	var acc;
-	var s;
-
-	acc = incrwstdev( 3.0 );
-
-	s = acc();
-	t.equal( s, null, 'returns null' );
+tape( 'the accumulator function ignores zero weights and only updates the weighted sample standard deviation after encountering a non-zero weight', function test( t ) {
+	var acc = incrwstdev();
+	t.equal( acc(), null, 'returns expected value' );
+	t.equal( acc( 2.0, 0.0 ), null, 'returns expected value' );
+	t.equal( acc( 2.0, 2.0 ), 0.0, 'returns expected value' );
+	t.equal( acc( 14.0, 2.0 ), 6.0, 'returns expected value' );
+	t.equal( acc( 25.0, 0.0 ), 6.0, 'returns expected value' );
+	t.end();
+});
 
-	s = acc( 3.0 );
-	t.notEqual( s, null, 'does not return null' );
+tape( 'the accumulator function throws an error if provided a second argument which is not a nonnegative number', function test( t ) {
+	var values;
+	var acc;
+	var i;
 
-	s = acc();
-	t.notEqual( s, null, 'does not return null' );
+	values = [
+		'5',
+		-5.0,
+		NaN,
+		undefined,
+		true,
+		false,
+		null,
+		void 0,
+		[],
+		{},
+		function noop() {}
+	];
 
+	for ( i = 0; i < values.length; i++ ) {
+		t.throws( badValue( values[i] ), TypeError, 'throws an error when provided '+values[i] );
+	}
 	t.end();
+
+	function badValue( value ) {
+		return function badValue() {
+			acc = incrwstdev();
+			acc( 2.0, value );
+		};
+	}
 });
 
 tape( 'the accumulator function incrementally computes a weighted sample standard deviation', function test( t ) {
@@ -176,13 +200,6 @@ tape( 'if not provided an input value, the accumulator function returns the curr
 	t.end();
 });
 
-tape( 'if not provided a weight, the accumulator function returns `NaN`', function test( t ) {
-	var acc = incrwstdev();
-	t.equal( isnan( acc( 2.0 ) ), true, 'returns NaN' );
-	t.equal( isnan( acc( 3.14 ) ), true, 'returns NaN' );
-	t.end();
-});
-
 tape( 'if provided `NaN` for a value, the accumulator function returns `NaN`', function test( t ) {
 	var acc = incrwstdev();
 	t.equal( isnan( acc( NaN, 1.0 ) ), true, 'returns NaN' );