docs(docs-infra): add testing-attribute-directives.en.md for the english version and translate testing-attribute-directives.md for spanish

Fixes #225

aio/content/guide/testing-attribute-directives.en.md

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+
+{@a attribute-directive}
+
+# Testing Attribute Directives
+
+An _attribute directive_ modifies the behavior of an element, component or another directive.
+Its name reflects the way the directive is applied: as an attribute on a host element.
+
+<div class="alert is-helpful">
+
+  For the sample app that the testing guides describe, see the <live-example name="testing" embedded-style noDownload>sample app</live-example>.
+
+  For the tests features in the testing guides, see <live-example name="testing" stackblitz="specs" noDownload>tests</live-example>.
+
+</div>
+
+## Testing the `HighlightDirective`
+
+The sample application's `HighlightDirective` sets the background color of an element
+based on either a data bound color or a default color (lightgray).
+It also sets a custom property of the element (`customProperty`) to `true`
+for no reason other than to show that it can.
+
+<code-example path="testing/src/app/shared/highlight.directive.ts" header="app/shared/highlight.directive.ts"></code-example>
+
+It's used throughout the application, perhaps most simply in the `AboutComponent`:
+
+<code-example path="testing/src/app/about/about.component.ts" header="app/about/about.component.ts"></code-example>
+
+Testing the specific use of the `HighlightDirective` within the `AboutComponent` requires only the techniques explored in the ["Nested component tests"](guide/testing-components-scenarios#nested-component-tests) section of [Component testing scenarios](guide/testing-components-scenarios).
+
+<code-example path="testing/src/app/about/about.component.spec.ts" region="tests" header="app/about/about.component.spec.ts"></code-example>
+
+However, testing a single use case is unlikely to explore the full range of a directive's capabilities.
+Finding and testing all components that use the directive is tedious, brittle, and almost as unlikely to afford full coverage.
+
+_Class-only tests_ might be helpful,
+but attribute directives like this one tend to manipulate the DOM.
+Isolated unit tests don't touch the DOM and, therefore,
+do not inspire confidence in the directive's efficacy.
+
+A better solution is to create an artificial test component that demonstrates all ways to apply the directive.
+
+<code-example path="testing/src/app/shared/highlight.directive.spec.ts" region="test-component" header="app/shared/highlight.directive.spec.ts (TestComponent)"></code-example>
+
+<div class="lightbox">
+  <img src='generated/images/guide/testing/highlight-directive-spec.png' alt="HighlightDirective spec in action">
+</div>
+
+<div class="alert is-helpful">
+
+The `<input>` case binds the `HighlightDirective` to the name of a color value in the input box.
+The initial value is the word "cyan" which should be the background color of the input box.
+
+</div>
+
+Here are some tests of this component:
+
+<code-example path="testing/src/app/shared/highlight.directive.spec.ts" region="selected-tests" header="app/shared/highlight.directive.spec.ts (selected tests)"></code-example>
+
+A few techniques are noteworthy:
+
+- The `By.directive` predicate is a great way to get the elements that have this directive _when their element types are unknown_.
+
+- The <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/:not">`:not` pseudo-class</a>
+  in `By.css('h2:not([highlight])')` helps find `<h2>` elements that _do not_ have the directive.
+  `By.css('*:not([highlight])')` finds _any_ element that does not have the directive.
+
+- `DebugElement.styles` affords access to element styles even in the absence of a real browser, thanks to the `DebugElement` abstraction.
+  But feel free to exploit the `nativeElement` when that seems easier or more clear than the abstraction.
+
+- Angular adds a directive to the injector of the element to which it is applied.
+  The test for the default color uses the injector of the second `<h2>` to get its `HighlightDirective` instance
+  and its `defaultColor`.
+
+- `DebugElement.properties` affords access to the artificial custom property that is set by the directive.
+
+<hr>