testing-dbt-models

What this skill does

# dbt Testing

**Every model deserves at least one test. Primary keys need unique + not_null.**

## Workflow

### 1. Study Existing Test Patterns

**CRITICAL: Match the project's existing testing style before adding new tests.**

```bash
# Find all schema.yml files with tests
find . -name "schema.yml" -exec grep -l "tests:" {} \;

# Read existing tests to learn patterns
cat models/staging/schema.yml | head -100
cat models/marts/schema.yml | head -100

# Check for custom tests or dbt packages
ls tests/
cat packages.yml 2>/dev/null
```

**Extract from existing tests:**
- YAML formatting style (indentation, spacing)
- Test coverage depth (all columns vs key columns only)
- Use of custom tests (dbt_utils, dbt_expectations, custom macros)
- Description style (brief vs detailed)
- Severity levels used (warn vs error)

### 2. Read Model SQL

```bash
cat models/<path>/<model_name>.sql
```

Identify: primary keys, foreign keys, categorical columns, date columns, business-critical fields.

### 3. Check Existing Tests for This Model

```bash
cat models/<path>/schema.yml | grep -A 50 "<model_name>"
# or
find . -name "schema.yml" -exec grep -l "<model_name>" {} \;
```

### 4. Identify Testable Columns

| Column Type | Recommended Tests |
|-------------|-------------------|
| Primary key | `unique`, `not_null` |
| Foreign key | `not_null`, `relationships` |
| Categorical | `accepted_values` (ask user for valid values) |
| Required field | `not_null` |
| Date/timestamp | `not_null` |
| Boolean | `accepted_values: [true, false]` |

### 5. Write Tests in schema.yml

**Match the existing style from step 1. Example format (adapt to project):**

```yaml
version: 2

models:
  - name: model_name
    description: "Brief description of what this model contains"
    columns:
      - name: primary_key_column
        description: "Unique identifier for this record"
        tests:
          - unique
          - not_null

      - name: foreign_key_column
        description: "Reference to related_model"
        tests:
          - not_null
          - relationships:
              to: ref('related_model')
              field: related_key_column

      - name: status
        description: "Current status of the record"
        tests:
          - not_null
          - accepted_values:
              values: ['pending', 'active', 'completed', 'cancelled']

      - name: created_at
        description: "Timestamp when record was created"
        tests:
          - not_null
```

### 6. Run Tests

```bash
# Test specific model
dbt test --select <model_name>

# Test with upstream
dbt test --select +<model_name>
```

### 7. Fix Failing Tests

Common failures and fixes:

| Failure | Likely Cause | Fix |
|---------|--------------|-----|
| `unique` fails | Duplicate records | Add deduplication in model |
| `not_null` fails | NULL values in source | Add COALESCE or filter |
| `relationships` fails | Orphan records | Add WHERE clause or fix upstream |
| `accepted_values` fails | New/unexpected values | Update accepted values list |

## Test Types Reference

### Generic Tests (built-in)

```yaml
tests:
  - unique
  - not_null
  - accepted_values:
      values: ['a', 'b', 'c']
  - relationships:
      to: ref('other_model')
      field: id
```

### Custom Generic Tests

```yaml
tests:
  - dbt_utils.expression_is_true:
      expression: "amount >= 0"
  - dbt_utils.recency:
      datepart: day
      field: created_at
      interval: 1
```

### Singular Tests

Create `tests/<test_name>.sql`:
```sql
-- tests/assert_positive_revenue.sql
select *
from {{ ref('orders') }}
where revenue < 0
```

## Anti-Patterns

- Adding tests without checking existing project patterns first
- Using different YAML formatting style than existing tests
- Models without any tests
- Primary keys without both unique AND not_null
- Testing only obvious columns, ignoring business-critical ones
- Hardcoding accepted_values without confirming with stakeholders
- Adding dbt_utils tests when project doesn't use that package