Merge pull request #92 from fishtown-analytics/expression-is-true-test

Add expression_is_true schema test

Author: drewbanin

README.md

@@ -93,6 +93,21 @@ models:
 
 ```
 
+#### expression_is_true ([source](macros/schema_tests/expression_is_true.sql))
+This schema test asserts that a valid sql expression is true for all records. This is useful when checking integrity across columns, for example, that a total is equal to the sum of its parts, or that at least one column is true.
+
+Usage:
+```yaml
+version: 2
+
+models:
+  - name: model_name
+    tests:
+      - dbt_utils.expression_is_true:
+          expression: "col_a + col_b = total"
+
+```
+
 #### recency ([source](macros/schema_tests/recency.sql))
 This schema test asserts that there is data in the referenced model at least as recent as the defined interval prior to the current timestamp.
 

integration_tests/data/schema_tests/data_test_expression_is_true.csv

@@ -0,0 +1,4 @@
+col_a,col_b
+0,1
+1,0
+0.5,0.5

integration_tests/models/schema_tests/schema.yml

@@ -13,6 +13,11 @@ models:
         tests:
           - dbt_utils.at_least_one
 
+  - name: data_test_expression_is_true
+    tests:
+      - dbt_utils.expression_is_true:
+          expression: col_a + col_b = 1
+        
   - name: test_recency
     tests:
       - dbt_utils.recency:

macros/schema_tests/expression_is_true.sql

@@ -0,0 +1,17 @@
+{% macro test_expression_is_true(model) %}
+
+{% set expression = kwargs.get('expression', kwargs.get('arg')) %}
+
+with validation_errors as (
+
+    select
+        *
+    from {{model}}
+    where not({{expression}})
+
+)
+
+select count(*)
+from validation_errors
+
+{% endmacro %}