Add tests to check from_string & from_spec equality

This will avoid errors like #27
popping up in future

Signed-off-by: Hritik Vijay <hritikxx8@gmail.com>

Author: Hritik14

tests/test_version_range.py

@@ -5,11 +5,13 @@
 # Visit https://aboutcode.org and https://github.com/nexB/univers for support and download.
 
 from unittest import TestCase
+import pytest
 
 from univers.version_constraint import VersionConstraint
 from univers.version_range import GemVersionRange
 from univers.version_range import PypiVersionRange
 from univers.version_range import VersionRange
+from univers.version_range import RANGE_CLASS_BY_SCHEMES
 from univers.versions import PypiVersion
 from univers.versions import RubygemsVersion
 
@@ -150,3 +152,19 @@ def test_GemVersionRange_from_native_range_with_pessimistic_operator(self):
             VersionConstraint(comparator=">=", version=RubygemsVersion(string="2.0.8")),
             VersionConstraint(comparator="<", version=RubygemsVersion(string="2.1")),
         )
+
+
+@pytest.mark.parametrize("scheme, range_class", RANGE_CLASS_BY_SCHEMES.items())
+class TestVersionRangeImplementations:
+    VERSION_RANGES_BY_SCHEMES = {
+        "nginx": ["0.8.40+", "0.7.52-0.8.39", "0.9.10", "1.5.0+, 1.4.1+"],
+    }
+
+    def test_from_native_and_from_string_equality(self, scheme, range_class):
+        if scheme not in self.VERSION_RANGES_BY_SCHEMES:
+            pytest.skip(f"No {scheme} in VERSION_RANGES_BY_SCHEMES")
+
+        for rng in self.VERSION_RANGES_BY_SCHEMES.get(scheme, []):
+            rng_from_native = range_class.from_native(rng)
+            rng_from_string = range_class.from_string(rng_from_native.to_string())
+            assert rng_from_native == rng_from_string