Return errors when found or None otherwise

This commit adds a number of functions that return the error object
when an error is found, or `None` otherwise. It avoids the use of
exceptions as control flow constructs.

1 files changed, 58 insertions, 0 deletions

diff --git a/tests/qc/test_header.py b/tests/qc/test_header.py
index 6ca9376..f860a71 100644
--- a/tests/qc/test_header.py
+++ b/tests/qc/test_header.py
@@ -4,7 +4,10 @@ from hypothesis import given
 from hypothesis import strategies as st
 
 from quality_control.headers import valid_header
+from quality_control.errors import InvalidValue, DuplicateHeading
 from quality_control.errors import DuplicateHeader, InvalidHeaderValue
+from quality_control.headers import (
+    invalid_header, invalid_headings, duplicate_headings)
 
 @given(headers=st.lists(st.text(max_size=10)))
 def test_valid_header_errors_with_invalid_headers(headers):
@@ -31,3 +34,58 @@ def test_valid_header_fails_with_duplicate_headers(strains, headers):
     """Check that parsing fails if any header is duplicated"""
     with pytest.raises(DuplicateHeader):
         valid_header(strains, headers)
+
+## ============================================================
+
+@given(headers=st.lists(st.text(max_size=10), max_size=1))
+def test_invalid_header_with_list_of_one_value(headers):
+    assert invalid_header(0, headers) == InvalidValue(
+        0, 0, "<TAB>".join(headers),
+        "The header MUST contain at least 2 columns")
+
+@given(headings=st.lists(st.text(min_size=2, max_size=10), min_size=2))
+def test_invalid_headings_with_invalid_inputs(headings):
+    "Verify that the check for header validity works"
+    assert invalid_headings(0, ("BXD1", "BXD2", "BXD3"), headings) == tuple(
+        InvalidValue(0, col, heading, f"'{heading}' not a valid strain.")
+        for col, heading in enumerate(headings, start=2))
+
+@pytest.mark.parametrize(
+    "strains,headers", [
+        (("BXD1", "BXD2", "BXD3"), ("ProbeSet", "BXD3", "BXD1")),
+        (("AStrain", "AnotherStrain", "YetAnotherStrain"),
+         ("Individual", "AStrain", "AnotherStrain", "YetAnotherStrain"))])
+def test_invalid_header_with_valid_headers(strains, headers):
+    "Verify that the check for header validity works"
+    assert invalid_header(0, headers) == None
+
+@pytest.mark.parametrize(
+    "strains,headings", [
+        (("BXD1", "BXD2", "BXD3"), ("BXD3", "BXD1")),
+        (("AStrain", "AnotherStrain", "YetAnotherStrain"),
+         ("AStrain", "AnotherStrain", "YetAnotherStrain"))])
+def test_invalid_headings_with_valid_headings(strains, headings):
+    "Verify that the check for header validity works"
+    assert invalid_headings(0, strains, headings) == tuple()
+
+@pytest.mark.parametrize(
+    "headers,repeated", [
+        (("ProbeSet", "BXD3", "BXD1", "BXD1"), {"BXD1": (3, 4)}),
+        (("Individual", "AStrain", "AnotherStrain", "YetAnotherStrain",
+          "AStrain"), {"AStrain": (2, 5)})])
+def test_duplicate_headers_with_repeated_column_headings(headers, repeated):
+    """Check that parsing fails if any header is duplicated"""
+    assert duplicate_headings(0, headers) == tuple(
+        DuplicateHeading(0, head, cols, (
+            f"Heading '{head}', is repeated in columns "
+            f"{','.join(str(i) for i in cols)}"))
+        for head, cols in repeated.items())
+
+@pytest.mark.parametrize(
+    "headers", [
+        (("ProbeSet", "BXD3", "BXD1")),
+        (("Individual", "AStrain", "AnotherStrain", "YetAnotherStrain",))])
+def test_duplicate_headers_with_unique_column_headings(headers):
+    """Check that parsing fails if any header is duplicated"""
+    assert duplicate_headings(0, headers) == tuple()
+