chore: Remove unused test files and scanner module

Author: andy1li

internal/assertions/stderr_assertion.go

@@ -27,26 +27,34 @@ func (a StderrAssertion) Run(result executable.ExecutableResult, logger *logger.
 			logAllSuccessLogs(successLogs, logger)
 
 			if skippedLines > 0 {
-				logger.Errorf("Skipped %d lines that didn't start with [line N]", skippedLines)
+				logger.Plainf("[stderr] Skipped %d lines that didn't start with [line N]", skippedLines)
 			}
 
-			return fmt.Errorf("Expected line #%d on stderr to be %q, but didn't find line", i+1, expectedLine)
+			return fmt.Errorf(`
+[stderr] Missing line #%d from stderr: %q
+[stderr] Perhaps it's printed to stdout? It should be printed to stderr.
+ `, i+1, expectedLine)
 		}
 		actualValue := stderr[i]
 
 		if actualValue != expectedLine {
 			logAllSuccessLogs(successLogs, logger)
-			logger.Errorf("𐄂 %s", actualValue)
-			return fmt.Errorf("Expected line #%d on stderr to be %q, got %q", i+1, expectedLine, actualValue)
+
+			return fmt.Errorf(`
+[stderr] Mismatch on line #%d of stderr:
+[stderr] Expected: %q
+[stderr] Actual  : %q
+ `, i+1, expectedLine, actualValue)
 		} else {
 			successLogs = append(successLogs, fmt.Sprintf("✓ %s", actualValue))
 		}
 	}
 
 	if len(stderr) > len(a.ExpectedLines) {
 		logAllSuccessLogs(successLogs, logger)
-		logger.Errorf("! %s", stderr[len(a.ExpectedLines)])
-		return fmt.Errorf("Expected last stderr line to be %q, but found extra line: %q", a.ExpectedLines[len(a.ExpectedLines)-1], stderr[len(a.ExpectedLines)])
+		return fmt.Errorf(`
+𐄂 [stderr] Extra line in stderr: %q
+ `, stderr[len(a.ExpectedLines)])
 	}
 
 	// If all lines match, we don't want to print all the lines again