add test for zero length variable name

parsing an environment file should give an error in case a zero-length
variable name (definition w/o a variable name) is encountered.

previously these lines went through unnoticed not informing the user about
a potential configuration error.

Signed-off-by: Tom Klingenberg <tklingenberg@lastflood.net>

opts/envfile_test.go

@@ -162,3 +162,17 @@ HOME
 		t.Fatal("exactly one variable is imported (as the other one is not set at all)")
 	}
 }
+
+// ParseEnvFile with empty variable name
+func TestParseEnvVariableWithNoNameFile(t *testing.T) {
+	content := `# comment=
+=blank variable names are an error case
+`
+	tmpFile := tmpFileWithContent(content, t)
+	defer os.Remove(tmpFile)
+
+	_, err := ParseEnvFile(tmpFile)
+	if nil == err {
+		t.Fatal("if a variable has no name parsing an environment file must fail")
+	}
+}