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Testing Attribute Directives
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An attribute directive modifies the behavior of an element, component or another directive.\nIts name reflects the way the directive is applied: as an attribute on a host element.
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For the sample app that the testing guides describe, see the sample app.
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For the tests features in the testing guides, see tests.
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Testing the HighlightDirective
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The sample application's HighlightDirective sets the background color of an element\nbased on either a data bound color or a default color (lightgray).\nIt also sets a custom property of the element (customProperty) to true\nfor no reason other than to show that it can.
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\nimport { Directive, ElementRef, Input, OnChanges } from '@angular/core';\n\n@Directive({ selector: '[highlight]' })\n/**\n * Set backgroundColor for the attached element to highlight color\n * and set the element's customProperty to true\n */\nexport class HighlightDirective implements OnChanges {\n\n defaultColor = 'rgb(211, 211, 211)'; // lightgray\n\n @Input('highlight') bgColor: string;\n\n constructor(private el: ElementRef) {\n el.nativeElement.style.customProperty = true;\n }\n\n ngOnChanges() {\n this.el.nativeElement.style.backgroundColor = this.bgColor || this.defaultColor;\n }\n}\n\n\n\n
It's used throughout the application, perhaps most simply in the AboutComponent:
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\nimport { Component } from '@angular/core';\n@Component({\n template: `\n <h2 highlight=\"skyblue\">About</h2>\n <h3>Quote of the day:</h3>\n <twain-quote></twain-quote>\n `\n})\nexport class AboutComponent { }\n\n\n\n
Testing the specific use of the HighlightDirective within the AboutComponent requires only the techniques explored in the \"Nested component tests\" section of Component testing scenarios.
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\nbeforeEach(() => {\n fixture = TestBed.configureTestingModule({\n declarations: [ AboutComponent, HighlightDirective ],\n schemas: [ NO_ERRORS_SCHEMA ]\n })\n .createComponent(AboutComponent);\n fixture.detectChanges(); // initial binding\n});\n\nit('should have skyblue <h2>', () => {\n const h2: HTMLElement = fixture.nativeElement.querySelector('h2');\n const bgColor = h2.style.backgroundColor;\n expect(bgColor).toBe('skyblue');\n});\n\n\n
However, testing a single use case is unlikely to explore the full range of a directive's capabilities.\nFinding and testing all components that use the directive is tedious, brittle, and almost as unlikely to afford full coverage.
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Class-only tests might be helpful,\nbut attribute directives like this one tend to manipulate the DOM.\nIsolated unit tests don't touch the DOM and, therefore,\ndo not inspire confidence in the directive's efficacy.
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A better solution is to create an artificial test component that demonstrates all ways to apply the directive.
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\n@Component({\n template: `\n <h2 highlight=\"yellow\">Something Yellow</h2>\n <h2 highlight>The Default (Gray)</h2>\n <h2>No Highlight</h2>\n <input #box [highlight]=\"box.value\" value=\"cyan\"/>`\n})\nclass TestComponent { }\n\n\n
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![\"HighlightDirective](\"generated/images/guide/testing/highlight-directive-spec.png\")
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The <input> case binds the HighlightDirective to the name of a color value in the input box.\nThe initial value is the word \"cyan\" which should be the background color of the input box.
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Here are some tests of this component:
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\nbeforeEach(() => {\n fixture = TestBed.configureTestingModule({\n declarations: [ HighlightDirective, TestComponent ]\n })\n .createComponent(TestComponent);\n\n fixture.detectChanges(); // initial binding\n\n // all elements with an attached HighlightDirective\n des = fixture.debugElement.queryAll(By.directive(HighlightDirective));\n\n // the h2 without the HighlightDirective\n bareH2 = fixture.debugElement.query(By.css('h2:not([highlight])'));\n});\n\n// color tests\nit('should have three highlighted elements', () => {\n expect(des.length).toBe(3);\n});\n\nit('should color 1st <h2> background \"yellow\"', () => {\n const bgColor = des[0].nativeElement.style.backgroundColor;\n expect(bgColor).toBe('yellow');\n});\n\nit('should color 2nd <h2> background w/ default color', () => {\n const dir = des[1].injector.get(HighlightDirective) as HighlightDirective;\n const bgColor = des[1].nativeElement.style.backgroundColor;\n expect(bgColor).toBe(dir.defaultColor);\n});\n\nit('should bind <input> background to value color', () => {\n // easier to work with nativeElement\n const input = des[2].nativeElement as HTMLInputElement;\n expect(input.style.backgroundColor).toBe('cyan', 'initial backgroundColor');\n\n input.value = 'green';\n\n // Dispatch a DOM event so that Angular responds to the input value change.\n // In older browsers, such as IE, you might need a CustomEvent instead. See\n // https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent/CustomEvent#Polyfill\n input.dispatchEvent(new Event('input'));\n fixture.detectChanges();\n\n expect(input.style.backgroundColor).toBe('green', 'changed backgroundColor');\n});\n\n\nit('bare <h2> should not have a customProperty', () => {\n expect(bareH2.properties.customProperty).toBeUndefined();\n});\n\n\n
A few techniques are noteworthy:
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The By.directive predicate is a great way to get the elements that have this directive when their element types are unknown.
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The :not pseudo-class\nin By.css('h2:not([highlight])') helps find <h2> elements that do not have the directive.\nBy.css('*:not([highlight])') finds any element that does not have the directive.
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DebugElement.styles affords access to element styles even in the absence of a real browser, thanks to the DebugElement abstraction.\nBut feel free to exploit the nativeElement when that seems easier or more clear than the abstraction.
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Angular adds a directive to the injector of the element to which it is applied.\nThe test for the default color uses the injector of the second <h2> to get its HighlightDirective instance\nand its defaultColor.
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DebugElement.properties affords access to the artificial custom property that is set by the directive.
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