42 lines
1.6 KiB
Markdown
42 lines
1.6 KiB
Markdown
# Testing Pipes
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You can test [pipes](guide/pipes) without the Angular testing utilities.
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<div class="alert is-helpful">
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For the sample application that the testing guides describe, see the <live-example name="testing" embedded-style noDownload>sample app</live-example>.
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For the tests features in the testing guides, see <live-example name="testing" stackblitz="specs" noDownload>tests</live-example>.
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</div>
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## Testing the `TitleCasePipe`
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A pipe class has one method, `transform`, that manipulates the input
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value into a transformed output value.
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The `transform` implementation rarely interacts with the DOM.
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Most pipes have no dependence on Angular other than the `@Pipe`
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metadata and an interface.
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Consider a `TitleCasePipe` that capitalizes the first letter of each word.
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Here's an implementation with a regular expression.
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<code-example path="testing/src/app/shared/title-case.pipe.ts" header="app/shared/title-case.pipe.ts"></code-example>
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Anything that uses a regular expression is worth testing thoroughly.
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Use simple Jasmine to explore the expected cases and the edge cases.
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<code-example path="testing/src/app/shared/title-case.pipe.spec.ts" region="excerpt" header="app/shared/title-case.pipe.spec.ts"></code-example>
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{@a write-tests}
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## Writing DOM tests to support a pipe test
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These are tests of the pipe _in isolation_.
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They can't tell if the `TitleCasePipe` is working properly as applied in the application components.
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Consider adding component tests such as this one:
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<code-example path="testing/src/app/hero/hero-detail.component.spec.ts" region="title-case-pipe" header="app/hero/hero-detail.component.spec.ts (pipe test)"></code-example>
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