Adds new lint function for empty env files

New function that raises a failure if the size of
the environment file, if this one exists, is zero.

Signed-off-by: mcasquer <mcasquer@redhat.com>

tmt/base.py

@@ -2130,6 +2130,22 @@ def lint_unknown_keys(self) -> LinterReturn:
 
         yield LinterOutcome.PASS, 'correct keys are used'
 
+    def lint_empty_env_files(self) -> LinterReturn:
+        """ P001: env files are not empty """
+
+        env_files = self.node.get("environment-file") or []
+        if len(env_files) > 0:
+            for env_file in env_files:
+                path = os.path.normpath(env_file)
+                size = os.path.getsize(path)
+
+                if (path is not None and size == 0):
+                    yield LinterOutcome.FAIL, f'the file "{env_file}" is empty'
+
+                    return
+
+        yield LinterOutcome.PASS, 'no empty environment files found'
+
     def lint_execute_not_defined(self) -> LinterReturn:
         """ P002: execute step must be defined with "how" """