Fix type narrowing for non empty array assert

source/index.ts

@@ -575,7 +575,7 @@ type Assert = {
 	nodeStream: (value: unknown) => asserts value is NodeStream;
 	infinite: (value: unknown) => asserts value is number;
 	emptyArray: (value: unknown) => asserts value is never[];
-	nonEmptyArray: (value: unknown) => asserts value is [unknown, ...unknown[]];
+	nonEmptyArray: <T = unknown>(value: T | T[]) => asserts value is [T, ...T[]];
 	emptyString: (value: unknown) => asserts value is '';
 	emptyStringOrWhitespace: (value: unknown) => asserts value is string;
 	nonEmptyString: (value: unknown) => asserts value is string;
@@ -681,7 +681,7 @@ export const assert: Assert = {
 	nodeStream: (value: unknown): asserts value is NodeStream => assertType(is.nodeStream(value), AssertionTypeDescription.nodeStream, value),
 	infinite: (value: unknown): asserts value is number => assertType(is.infinite(value), AssertionTypeDescription.infinite, value),
 	emptyArray: (value: unknown): asserts value is never[] => assertType(is.emptyArray(value), AssertionTypeDescription.emptyArray, value),
-	nonEmptyArray: (value: unknown): asserts value is [unknown, ...unknown[]] => assertType(is.nonEmptyArray(value), AssertionTypeDescription.nonEmptyArray, value),
+	nonEmptyArray: <T = unknown>(value: T | T[]): asserts value is [T, ...T[]] => assertType(is.nonEmptyArray(value), AssertionTypeDescription.nonEmptyArray, value),
 	emptyString: (value: unknown): asserts value is '' => assertType(is.emptyString(value), AssertionTypeDescription.emptyString, value),
 	emptyStringOrWhitespace: (value: unknown): asserts value is string => assertType(is.emptyStringOrWhitespace(value), AssertionTypeDescription.emptyStringOrWhitespace, value),
 	nonEmptyString: (value: unknown): asserts value is string => assertType(is.nonEmptyString(value), AssertionTypeDescription.nonEmptyString, value),

test/test.ts

@@ -1477,6 +1477,36 @@ test('is.nonEmptyArray', t => {
 			function_(value);
 		}
 	}
+
+	{
+		const strings = ['🦄', 'unicorn'];
+		const function_ = (value: string) => value;
+
+		assert.nonEmptyArray(strings);
+
+		const value = strings[0];
+		function_(value);
+	}
+
+	{
+		const mixed = ['🦄', 'unicorn', 1, 2];
+		const function_ = (value: string | number) => value;
+
+		assert.nonEmptyArray(mixed);
+
+		const value = mixed[0];
+		function_(value);
+	}
+
+	{
+		const arrays = [['🦄'], ['unicorn']];
+		const function_ = (value: string[]) => value;
+
+		assert.nonEmptyArray(arrays);
+
+		const value = arrays[0];
+		function_(value);
+	}
 });
 
 test('is.emptyString', t => {