Adds new 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 <[email protected]>

tmt/base.py

@@ -2130,6 +2130,18 @@ def lint_unknown_keys(self) -> LinterReturn:
 
         yield LinterOutcome.PASS, 'correct keys are used'
 
+    def lint_empty_env_files(self) -> LinterReturn:
+        """ P001: all files are not empty """
+
+        env_file = self.plan_environment_file
+
+        if (self.my_run and env_file.exists() and env_file.stat().st_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" """