required sample size is zero (#69)

setup.cfg

@@ -1,6 +1,6 @@
 [metadata]
 name = ep-stats
-version = 2.3.0
+version = 2.3.1
 description = Statistical package to evaluate ab tests in experimentation platform.
 long_description = file: README.md
 long_description_content_type = text/markdown

src/epstats/toolkit/parser.py

@@ -206,6 +206,8 @@ def __str__(self):
         return f"{self.value}"
 
     def evaluate_agg(self, goals):
+        # n_variants = goals["exp_variant_id"].nunique()
+        # return [self.value] * n_variants
         return self.value
 
     def evaluate_by_unit(self, goals):

src/epstats/toolkit/statistics.py

@@ -417,7 +417,7 @@ def power_from_required_sample_size_per_variant(
             power
         """
 
-        if n_variants < 2:
+        if n_variants < 2 or required_sample_size_per_variant == 0:
             return np.nan
 
         required_sample_size_ratio = sample_size_per_variant / required_sample_size_per_variant

tests/epstats/toolkit/test_statistics.py

@@ -238,3 +238,23 @@ def test_power_from_required_sample_size_per_variant_nan_params():
             required_sample_size_per_variant=np.nan,
         )
     )
+
+
+@pytest.mark.parametrize(
+    "args",
+    [
+        {
+            "n_variants": 1,
+            "sample_size_per_variant": 100,
+            "required_sample_size_per_variant": 100,
+        },
+        {
+            "n_variants": 2,
+            "sample_size_per_variant": 0,
+            "required_sample_size_per_variant": 0,
+        },
+    ],
+)
+def test_power_from_required_sample_size_per_variant_is_nan(args):
+
+    assert np.isnan(Statistics.power_from_required_sample_size_per_variant(**args))