docs/get-started/sdk/learn/components/component-tests.md

# Component tests

<<../../../_common/components/_tests_intro.md>>

## Test runners

Test runners are reusable adapters between the Test Runner Framework and common
frameworks used by developers to write tests in their preferred
language. Each test runner component exposes the `fuchsia.test.Suite` capability
that enables the `test_manager` to enumerate and execute individual tests, and
declares the appropriate execution `runner` with test framework support.

```json5
{
    // Execute tests using language-specific runner
    program: { runner: "elf_test_runner", },
    // Expose test suite protocol to test manager
    capabilities: [
        { protocol: "fuchsia.test.Suite" },
    ],
    expose: [
        {
            protocol: "fuchsia.test.Suite",
            from: "self",
        },
    ],
}
```

To simplify integration, the Test Runner Framework provides **manifest shards**
for each language-specific runner. The following is an equivalent test runner
CML for declaring the capabilities from the previous example component tests.

```json5
{
    include: [ "sys/testing/elf_test_runner.shard.cml" ]
}
```

Note: For complete details on the Test Runner Framework and component testing,
see the
[testing documentation](/docs/development/testing/components/test_runner_framework.md).

## Unit tests

[Unit testing](https://en.wikipedia.org/wiki/Unit_testing){:.external} focuses
on validating the individual units of code within your component and isolated
from other components on the system. Unit tests should be **hermetic**, meaning
that they do not require or provide additional capabilities outside of the test.

The Fuchsia SDK provides additional templates to facilitate unit testing
components:

* `cc_test()`: Compiles the C++ source code into a test binary.
* `fuchsia_test_component()`: Generates a Fuchsia component containing tests.
  You can combine multiple test components into the same `fuchsia_package()`.

Below is an example `BUILD.bazel` snippet for including unit tests:

```bazel
load(
    "fuchsia_cc_binary",
    "fuchsia_package",
    "fuchsia_test_component",
)

cc_test(
    name = "hello_world_test",
    srcs = [
        "hello_world_test.cc",
    ],
)

fuchsia_test_component(
  name = "unit_test_component",
  test_name = "hello_world_test",
  deps = [
      ":hello_world_test",
  ],
)

fuchsia_package(
    name = "unit_test_pkg",
    visibility = ["//visibility:public"],
    deps = [
      ":unit_test_component",
    ],
)
```

## Exercise: Echo unit tests

In this exercise, you'll add unit tests to the `echo` component with the
Test Runner Framework and run those tests in a FEMU environment.

### Implement unit tests

Unit tests verify that the internal functions of the component behave as
expected. For the `echo` component, you'll validate that the `greeting()`
function used in the previous exercise returns the expected values.

Add the following unit test functions to validate the behavior of the
`greeting()` function when supplied with one, two, or three arguments:

`echo/echo_unittest.cc`:

```
{% includecode gerrit_repo="fuchsia/sdk-samples/getting-started" gerrit_path="src/echo/echo_unittest.cc" region_tag="imports" adjust_indentation="auto" %}

#include "echo_component.h"

{% includecode gerrit_repo="fuchsia/sdk-samples/getting-started" gerrit_path="src/echo/echo_unittest.cc" region_tag="test_mod" adjust_indentation="auto" %}
```

### Run the unit tests

Add the following to your `BUILD.bazel` file to include your tests in the build
configuration:

`BUILD.bazel`:

```bazel
{% includecode gerrit_repo="fuchsia/sdk-samples/getting-started" gerrit_path="src/echo/BUILD.bazel" region_tag="imports" adjust_indentation="auto" %}

# ...

{% includecode gerrit_repo="fuchsia/sdk-samples/getting-started" gerrit_path="src/echo/BUILD.bazel" region_tag="unittest" adjust_indentation="auto" %}
```

This rule packages your unit tests into a component with the following URL:

```none
fuchsia-pkg://fuchsiasamples.com/echo_unittests#meta/echo_unittests.cm
```

Run `bazel build` and verify that the build completes successfully:

```posix-terminal
bazel build --config=fuchsia_x64 //fuchsia-codelab/echo:test_pkg \
    --publish_to=$HOME/.package_repos/sdk-samples
```

Use the `ffx test` command to execute the unit tests inside this package.
Verify that the tests pass:

```posix-terminal
ffx test run \
    fuchsia-pkg://fuchsiasamples.com/echo_unittests#meta/echo_unittests.cm
```