hasStyle: Throw an error if expectation object is empty

Author: Turbo87

lib/__tests__/does-not-have-style.ts

@@ -109,4 +109,10 @@ describe('assert.dom(...).doesNotHaveStyle()', () => {
       'Unexpected Parameter: [object Document]'
     );
   });
+
+  test('throws for empty expectation object', () => {
+    expect(() => assert.dom('div').doesNotHaveStyle({})).toThrow(
+      'Missing style expectations. There must be at least one style property in the passed in expectation object.'
+    );
+  });
 });

lib/__tests__/has-style.ts

@@ -106,4 +106,10 @@ describe('assert.dom(...).hasStyle()', () => {
       'Unexpected Parameter: [object Document]'
     );
   });
+
+  test('throws for empty expectation object', () => {
+    expect(() => assert.dom('div').hasStyle({})).toThrow(
+      'Missing style expectations. There must be at least one style property in the passed in expectation object.'
+    );
+  });
 });

lib/assertions.ts

@@ -600,6 +600,12 @@ export default class DOMAssertions {
 
     let computedStyle = window.getComputedStyle(element, selector);
     let expectedProperties = Object.keys(expected) as [keyof CSSStyleDeclaration];
+    if (expectedProperties.length <= 0) {
+      throw new TypeError(
+        `Missing style expectations. There must be at least one style property in the passed in expectation object.`
+      );
+    }
+
     let result = expectedProperties.every(
       property => computedStyle[property] === expected[property]
     );
@@ -666,6 +672,12 @@ export default class DOMAssertions {
     let computedStyle = window.getComputedStyle(element, selector);
 
     let expectedProperties = Object.keys(expected) as [keyof CSSStyleDeclaration];
+    if (expectedProperties.length <= 0) {
+      throw new TypeError(
+        `Missing style expectations. There must be at least one style property in the passed in expectation object.`
+      );
+    }
+
     let result = expectedProperties.some(
       property => computedStyle[property] !== expected[property]
     );