---
title: Policy Testing
kind: documentation
weight: 3
restrictedtoc: true
---

OPA gives you a high-level declarative language
([Rego](../policy-language)) to author fine-grained policies that
codify important requirements in your system.

To help you verify the correctness of your policies, OPA also gives you a
framework that you can use to write _tests_ for your policies. By writing
tests for your policies you can speed up the development process of new rules
and reduce the amount of time it takes to modify rules as requirements evolve.

## Getting Started

Let's use an example to get started. The file below implements a simple
policy that allows new users to be created and users to access their own
profile.

**example.rego**:

```live:example:module:read_only,openable
package authz

allow {
    input.path == ["users"]
    input.method == "POST"
}

allow {
    some profile_id
    input.path = ["users", profile_id]
    input.method == "GET"
    profile_id == input.user_id
}
```

To test this policy, we will create a separate Rego file that contains test cases.

**example_test.rego**:

```live:example/test:module:read_only,openable
package authz

test_post_allowed {
    allow with input as {"path": ["users"], "method": "POST"}
}

test_get_anonymous_denied {
    not allow with input as {"path": ["users"], "method": "GET"}
}

test_get_user_allowed {
    allow with input as {"path": ["users", "bob"], "method": "GET", "user_id": "bob"}
}

test_get_another_user_denied {
    not allow with input as {"path": ["users", "bob"], "method": "GET", "user_id": "alice"}
}
```

Both of these files are saved in the same directory.

```bash
$ ls
example.rego      example_test.rego
```

To exercise the policy, run the `opa test` command in the directory containing the files.

```bash
$ opa test . -v
data.authz.test_post_allowed: PASS (1.417µs)
data.authz.test_get_anonymous_denied: PASS (426ns)
data.authz.test_get_user_allowed: PASS (367ns)
data.authz.test_get_another_user_denied: PASS (320ns)
--------------------------------------------------------------------------------
PASS: 4/4
```

The `opa test` output indicates that all of the tests passed.

Try exercising the tests a bit more by removing the first rule in **example.rego**.

```bash
$ opa test . -v
FAILURES
--------------------------------------------------------------------------------
data.authz.test_post_allowed: FAIL (277.306µs)

  query:1                 Enter data.authz.test_post_allowed = _
  example_test.rego:3     | Enter data.authz.test_post_allowed
  example_test.rego:4     | | Fail data.authz.allow with input as {"method": "POST", "path": ["users"]}
  query:1                 | Fail data.authz.test_post_allowed = _

SUMMARY
--------------------------------------------------------------------------------
data.authz.test_post_allowed: FAIL (277.306µs)
data.authz.test_get_anonymous_denied: PASS (124.287µs)
data.authz.test_get_user_allowed: PASS (242.2µs)
data.authz.test_get_another_user_denied: PASS (131.964µs)
--------------------------------------------------------------------------------
PASS: 3/4
FAIL: 1/4
```

## Test Format

Tests are expressed as standard Rego rules with a convention that the rule
name is prefixed with `test_`.

```live:example_format:module:read_only
package mypackage

test_some_descriptive_name {
    # test logic
}
```

## Test Discovery

The `opa test` subcommand runs all of the tests (i.e., rules prefixed with
`test_`) found in Rego files passed on the command line. If directories are
passed as command line arguments, `opa test` will load their file contents
recursively.

## Specifying Tests to Run

The `opa test` subcommand supports a `--run`/`-r` regex option to further
specify which of the discovered tests should be evaluated. The option supports
[re2 syntax](https://github.com/google/re2/wiki/Syntax)

## Test Results

If the test rule is undefined or generates a non-`true` value the test result
is reported as `FAIL`. If the test encounters a runtime error (e.g., a divide
by zero condition) the test result is marked as an `ERROR`. Otherwise, the
test result is marked as `PASS`.

**pass_fail_error_test.rego**:

```live:example_results:module:read_only
package example

# This test will pass.
test_ok {
    true
}

# This test will fail.
test_failure {
    1 == 2
}

# This test will error.
test_error {
    1 / 0
}
```

By default, `opa test` reports the number of tests executed and displays all
of the tests that failed or errored.

```bash
$ opa test pass_fail_error_test.rego
data.example.test_failure: FAIL (253ns)
data.example.test_error: ERROR (289ns)
  pass_fail_error_test.rego:15: eval_builtin_error: div: divide by zero
--------------------------------------------------------------------------------
PASS: 1/3
FAIL: 1/3
ERROR: 1/3
```

By default, OPA prints the test results in a human-readable format. If you
need to consume the test results programmatically, use the JSON output format.

```bash
$ opa test --format=json pass_fail_error_test.rego
```

```json
[
  {
    "location": {
      "file": "pass_fail_error_test.rego",
      "row": 4,
      "col": 1
    },
    "package": "data.example",
    "name": "test_ok",
    "duration": 618515
  },
  {
    "location": {
      "file": "pass_fail_error_test.rego",
      "row": 9,
      "col": 1
    },
    "package": "data.example",
    "name": "test_failure",
    "fail": true,
    "duration": 322177
  },
  {
    "location": {
      "file": "pass_fail_error_test.rego",
      "row": 14,
      "col": 1
    },
    "package": "data.example",
    "name": "test_error",
    "error": {
      "code": "eval_internal_error",
      "message": "div: divide by zero",
      "location": {
        "file": "pass_fail_error_test.rego",
        "row": 15,
        "col": 5
      }
    },
    "duration": 345148
  }
]
```

## Data Mocking

OPA's `with` keyword can be used to replace the data document. Both base and virtual documents can be replaced. Below is a simple policy that depends on the data document.

**authz.rego**:

```live:with_keyword:module:read_only,openable
package authz

allow {
    x := data.policies[_]
    x.name == "test_policy"
    matches_role(input.role)
}

matches_role(my_role) {
    data.roles[my_role][_] == input.user
}
```

Below is the Rego file to test the above policy.

**authz_test.rego**:

```live:with_keyword/tests:module:read_only,openable
package authz

policies = [{"name": "test_policy"}]
roles = {"admin": ["alice"]}

test_allow_with_data {
    allow with input as {"user": "alice", "role": "admin"}  with data.policies as policies  with data.roles as roles
}
```

To exercise the policy, run the `opa test` command.

```bash
$ opa test -v authz.rego authz_test.rego
data.authz.test_allow_with_data: PASS (697ns)
--------------------------------------------------------------------------------
PASS: 1/1
```

Below is an example to replace a rule without arguments.

**authz.rego**:

```live:with_keyword_rules:module:read_only
package authz

allow1 {
    allow2
}

allow2 {
    2 == 1
}
```

**authz_test.rego**:

```live:with_keyword_rules/tests:module:read_only
package authz

test_replace_rule {
    allow1 with allow2 as true
}
```

```bash
$  opa test -v authz.rego authz_test.rego
data.authz.test_replace_rule: PASS (328ns)
--------------------------------------------------------------------------------
PASS: 1/1
```

Functions cannot be replaced by the `with` keyword. For example, in the below policy the function `cannot_replace` cannot be replaced.

**authz.rego**:

```live:with_keyword_funcs:module:read_only
package authz

invalid_replace {
    cannot_replace(input.label)
}

cannot_replace(label) {
    label == "test_label"
}
```

**authz_test.rego**:

```live:with_keyword_funcs/tests:module:read_only
package authz

test_invalid_replace {
    invalid_replace with input as {"label": "test_label"} with cannot_replace as true
}
```

```bash
$ opa test -v authz.rego authz_test.rego
1 error occurred: authz_test.rego:4: rego_compile_error: with keyword cannot replace functions
```


## Coverage

In addition to reporting pass, fail, and error results for tests, `opa test`
can also report _coverage_ for the policies under test.

The coverage report includes all of the lines evaluated and not evaluated in
the Rego files provided on the command line. When a line is not covered it
indicates one of two things:

* If the line refers to the head of a rule, the body of the rule was never true.
* If the line refers to an expression in a rule, the expression was never evaluated.

If we run the coverage report on the original **example.rego** file without
`test_get_user_allowed` from **example_test**.rego the report will indicate
that line 8 is not covered.

```bash
opa test --coverage --format=json example.rego example_test.rego
```

```json
{
  "files": {
    "example.rego": {
      "covered": [
        {
          "start": {
            "row": 3
          },
          "end": {
            "row": 5
          }
        },
        {
          "start": {
            "row": 9
          },
          "end": {
            "row": 11
          }
        }
      ],
      "not_covered": [
        {
          "start": {
            "row": 8
          },
          "end": {
            "row": 8
          }
        }
      ]
    },
    "example_test.rego": {
      "covered": [
        {
          "start": {
            "row": 3
          },
          "end": {
            "row": 4
          }
        },
        {
          "start": {
            "row": 7
          },
          "end": {
            "row": 8
          }
        },
        {
          "start": {
            "row": 11
          },
          "end": {
            "row": 12
          }
        }
      ]
    }
  }
}
```

