docs/content/code-security/codeql-cli/using-the-codeql-cli/testing-custom-queries.md

---
title: Testing custom queries
intro: 'You can set up tests for your {% data variables.product.prodname_codeql %} queries to ensure that they continue to return the expected results with new releases of the {% data variables.product.prodname_codeql_cli %}.'
product: '{% data reusables.gated-features.codeql %}'
versions:
  feature: codeql-packs
topics:
  - Advanced Security
  - Code scanning
  - CodeQL
redirect_from:
  - /code-security/codeql-cli/testing-custom-queries
---

{% data reusables.codeql-cli.codeql-site-migration-note %}

## About testing custom queries

{% data variables.product.prodname_codeql %} provides a simple test framework for automated regression testing
of queries. Test your queries to ensure that they behave as expected.

During a query test, {% data variables.product.prodname_codeql %} compares the results the user expects
the query to produce with those actually produced. If the expected and
actual results differ, the query test fails. To fix the test, you should iterate
on the query and the expected results until the actual results and the expected
results exactly match. This topic shows you how to create test files and execute
tests on them using the `test run` subcommand.

## Setting up a test {% data variables.product.prodname_codeql %} pack for custom queries

All {% data variables.product.prodname_codeql %} tests must be stored in a special "test" {% data variables.product.prodname_codeql %} pack. That is, a directory for test files with a `qlpack.yml` file that defines:

```yaml
name: <name-of-test-pack>
version: 0.0.0
dependencies:
  <codeql-libraries-and-queries-to-test>: "*"
extractor: <language-of-code-to-test>
```

The `dependencies` value specifies the {% data variables.product.prodname_codeql %} packs containing queries to test.
Typically, these packs will be resolved from source, and so it is not necessary
to specify a fixed version of the pack. The `extractor` defines which language the CLI will use to create test databases from the code files stored in this {% data variables.product.prodname_codeql %} pack. For more information, see "[About {% data variables.product.prodname_codeql %} packs](/code-security/codeql-cli/codeql-cli-reference/about-codeql-packs)."

You may find it useful to look at the way query tests are organized in the [{% data variables.product.prodname_codeql %} repository](https://github.com/github/codeql). Each language has a `src` directory, `ql/<language>/ql/src`, that contains libraries and queries for analyzing codebases. Alongside the `src` directory, there is a `test` directory with tests for
these libraries and queries.

Each `test` directory is configured as a test {% data variables.product.prodname_codeql %} pack with two subdirectories:

- `query-tests` a series of subdirectories with tests for queries stored in the `src` directory. Each subdirectory contains test code and a QL reference file that specifies the query to test.
- `library-tests` a series of subdirectories with tests for QL library files. Each subdirectory contains test code and queries that were written as unit tests for a library.

After creating the `qlpack.yml` file, you need to make sure that all of the dependencies are downloaded and available to the CLI. Do this by running the following command in the same directory as the `qlpack.yml` file:

```
codeql pack install
```

This will generate a `codeql-pack.lock.yml` file that specifies all of the transitive dependencies required to run queries in this pack. This file should be checked in to source control.

## Setting up the test files for a query

For each query you want to test, you should create a sub-directory in the test {% data variables.product.prodname_codeql %} pack.
Then add the following files to the subdirectory before you run the test command:

- A query reference file (`.qlref` file) defining the location of the query to test. The location is defined relative to the root of the {% data variables.product.prodname_codeql %} pack that contains the query. Usually, this is a {% data variables.product.prodname_codeql %} pack specified in the `dependencies` block of the test pack. For more information, see "[Query reference files](/code-security/codeql-cli/codeql-cli-reference/query-reference-files)."

   You do not need to add a query reference file if the query you want to test is stored in the test directory, but it is generally good practice to store queries separately from tests. The only exception is unit tests for QL libraries, which tend to be stored in test packs, separate from queries that generate alerts or paths.

- The example code you want to run your query against. This should consist of one or more files containing examples of the code the query is designed to identify.

You can also define the results you expect to see when you run the query against
the example code, by creating a file with the extension `.expected`. Alternatively, you can leave the test command to create the `.expected` file for you.

For an example showing how to create and test a query, see the [example](#example) below.

{% note %}

**Important:** Your `.ql`, `.qlref`, and `.expected` files must have consistent names.

If you want to directly specify the `.ql` file itself in the test command, it must have the same base name as the corresponding `.expected` file. For example, if the query is `MyJavaQuery.ql`, the expected results file must be `MyJavaQuery.expected`.

If you want to specify a `.qlref` file in the command, it must have the same base name as the corresponding `.expected` file, but the query itself may have a different name.

The names of the example code files don’t have to be consistent with the other test files. All example code files found next to the `.qlref` (or `.ql`) file and in any subdirectories will be used to create a test database. Therefore, for simplicity, we recommend you don’t save test files in directories that are ancestors of each other.

{% endnote %}

## Running `codeql test run`

{% data variables.product.prodname_codeql %} query tests are executed by running the following command:

```
codeql test run <test|dir>
```

The `<test|dir>` argument can be one or more of the following:

- Path to a `.ql` file.
- Path to a `.qlref` file that references a `.ql` file.
- Path to a directory that will be searched recursively for `.ql` and `.qlref` files.

You can also specify:

- `--threads:` optionally, the number of threads to use when running queries. The default option is `1`. You can specify more threads to speed up query execution. Specifying `0` matches the number of threads to the number of logical processors.

For full details of all the options you can use when testing queries, see "[AUTOTITLE](/code-security/codeql-cli/codeql-cli-manual/test-run)."

## Example

The following example shows you how to set up a test for a query that searches
Java code for `if` statements that have empty `then` blocks. It includes
steps to add the custom query and corresponding test files to separate {% data variables.product.prodname_codeql %} packs
outside your checkout of the {% data variables.product.prodname_codeql %} repository. This ensures when you update the
{% data variables.product.prodname_codeql %} libraries, or check out a different branch, you won’t overwrite your
custom queries and tests.

### Prepare a query and test files

1. Develop the query. For example, the following simple query finds empty `then`
blocks in Java code:

   ```
   import java

   from IfStmt ifstmt
   where ifstmt.getThen() instanceof EmptyStmt
   select ifstmt, "This if statement has an empty then."
   ```

1. Save the query to a file named `EmptyThen.ql` in a directory with your
other custom queries. For example, `custom-queries/java/queries/EmptyThen.ql`.

1. If you haven’t already added your custom queries to a {% data variables.product.prodname_codeql %} pack, create a {% data variables.product.prodname_codeql %} pack now. For example, if your custom Java queries are stored in `custom-queries/java/queries`, add a `qlpack.yml` file with the following contents to `custom-queries/java/queries`:

   ```yaml
   name: my-custom-queries
   dependencies:
     codeql/java-queries: "*"
   ```

   For more information about {% data variables.product.prodname_codeql %} packs, see "[About {% data variables.product.prodname_codeql %} packs](/code-security/codeql-cli/codeql-cli-reference/about-codeql-packs)."

1. Create a {% data variables.product.prodname_codeql %} pack for your Java tests by adding a `qlpack.yml` file with the following contents to `custom-queries/java/tests`, updating the `dependencies` to match the name of your {% data variables.product.prodname_codeql %} pack of custom queries:

{% indented_data_reference reusables.codeql-cli.test-qlpack spaces=2 %}

1. Run `codeql pack install` in the root of the test directory. This generates a `codeql-pack.lock.yml` file that specifies all of the transitive dependencies required to run queries in this pack.

1. Within the Java test pack, create a directory to contain the test files
associated with `EmptyThen.ql`. For example, `custom-queries/java/tests/EmptyThen`.

1. In the new directory, create `EmptyThen.qlref` to define the location of `EmptyThen.ql`. The path to the query must be specified relative to the root of
the {% data variables.product.prodname_codeql %} pack that contains the query. In this case, the query is in the
top level directory of the {% data variables.product.prodname_codeql %} pack named `my-custom-queries`,
which is declared as a dependency for `my-query-tests`. Therefore, `EmptyThen.qlref` should simply contain `EmptyThen.ql`.

1. Create a code snippet to test. The following Java code contains an empty `if` statement on the third line. Save it in `custom-queries/java/tests/EmptyThen/Test.java`.

  ```java
  class Test {
    public void problem(String arg) {
      if (arg.isEmpty())
        ;
      {
        System.out.println("Empty argument");
      }
    }

    public void good(String arg) {
      if (arg.isEmpty()) {
        System.out.println("Empty argument");
      }
    }
  }
  ```

### Execute the test

To execute the test, move into the `custom-queries` directory and run `codeql
test run java/tests/EmptyThen`.

When the test runs, it:

1. Finds one test in the `EmptyThen` directory.

1. Extracts a {% data variables.product.prodname_codeql %} database from the `.java` files stored in the `EmptyThen` directory.

1. Compiles the query referenced by the `EmptyThen.qlref` file.

   If this step fails, it’s because the CLI can’t find your custom {% data variables.product.prodname_codeql %} pack. Re-run the command and specify the location of your custom {% data variables.product.prodname_codeql %} pack, for example:

   `codeql test run --search-path=java java/tests/EmptyThen`

   For information about saving the search path as part of your configuration, see "[Specifying command options in a {% data variables.product.prodname_codeql %} configuration file](/code-security/codeql-cli/using-the-codeql-cli/specifying-command-options-in-a-codeql-configuration-file)."

1. Executes the test by running the query and generating an `EmptyThen.actual` results file.

1. Checks for an `EmptyThen.expected` file to compare with the `.actual` results file.

1. Reports the results of the test — in this case, a failure: `0 tests passed; 1 tests failed:`. The test failed because we haven’t yet added a file with the expected results of the query.

### View the query test output

{% data variables.product.prodname_codeql %} generates the following files in the `EmptyThen` directory:

- `EmptyThen.actual`, a file that contains the actual results generated by the
query.
- `EmptyThen.testproj`, a test database that you can load into VS Code and use to debug failing tests. When tests complete successfully, this database is deleted in a housekeeping step. You can override this step by running `test run` with the `--keep-databases` option.

In this case, the failure was expected and is easy to fix. If you open the `EmptyThen.actual` file, you can see the results of the test:

```

| Test.java:3:5:3:22 | stmt | This if statement has an empty then. |

```

This file contains a table, with a column for the location of the result,
along with separate columns for each part of the `select` clause the query outputs.
Since the results are what we expected, we can update the file extension to define
this as the expected result for this test (`EmptyThen.expected`).

If you rerun the test now, the output will be similar but it will finish by reporting: `All 1 tests passed.`.

If the results of the query change, for example, if you revise the `select` statement for the query, the test will fail. For failed results, the CLI output includes a unified diff of the `EmptyThen.expected` and `EmptyThen.actual` files.
This information may be sufficient to debug trivial test failures.

For failures that are harder to debug, you can import `EmptyThen.testproj`
into {% data variables.product.prodname_codeql %} for VS Code, execute `EmptyThen.ql`, and view the results in the
`Test.java` example code. For more information, see "[Analyzing your projects](https://codeql.github.com/docs/codeql-for-visual-studio-code/analyzing-your-projects/#analyzing-your-projects)" in the {% data variables.product.prodname_codeql %} for VS Code help.

## Further reading
- "[{% data variables.product.prodname_codeql %} queries](https://codeql.github.com/docs/writing-codeql-queries/codeql-queries/#codeql-queries)"
- "[Testing {% data variables.product.prodname_codeql %} queries in Visual Studio Code](https://codeql.github.com/docs/codeql-for-visual-studio-code/testing-codeql-queries-in-visual-studio-code/#testing-codeql-queries-in-visual-studio-code)."