The instrumented code for _commonprefix() function and a coverage tes…

…t for it

src/prompt_toolkit/completion/base.py

@@ -422,17 +422,30 @@ def get_suffix(completion: Completion) -> str:
     return _commonprefix([get_suffix(c) for c in completions2])
 
 
+# Data structures that hold coverage information about the conditional branches
+branch_coverage = {
+    "_commonprefix_1": False,  # Branch for checking if not strings
+    "_commonprefix_2": False,  # Branch for comparing characters
+    "_commonprefix_3": False,  # Branch for when the characters do not match
+}
+
 def _commonprefix(strings: Iterable[str]) -> str:
-    # Similar to os.path.commonprefix
     if not strings:
+        branch_coverage["_commonprefix_1"] = True
+        print("Branch 1 was hit")
         return ""
 
     else:
+        branch_coverage["_commonprefix_2"] = True
+        print("Branch 2 was hit")
         s1 = min(strings)
         s2 = max(strings)
 
         for i, c in enumerate(s1):
             if c != s2[i]:
+                branch_coverage["_commonprefix_3"] = True
+                print("Branch 3 was hit")
+                print("here")
                 return s1[:i]
 
         return s1

tests/test_commonprefix_coverage.py

@@ -0,0 +1,24 @@
+from __future__ import annotations
+from typing import Iterable, List, Tuple
+from prompt_toolkit.completion.base import branch_coverage,_commonprefix
+
+def print_coverage():
+    print("\nCoverage report:")
+    hit_branches = sum(branch_coverage.values())
+    total_branches = len(branch_coverage)
+    coverage_percentage = (hit_branches / total_branches) * 100
+    for branch, hit in branch_coverage.items():
+        print(f"{branch} was {'hit' if hit else 'not hit'}")
+    print(f"Coverage: {hit_branches}/{total_branches} branches hit ({coverage_percentage:.2f}%)\n")
+
+
+# Tests
+test_cases: List[Tuple[List[str], str]] = []
+
+for strings, description in test_cases:
+    print(f"\nTesting case: {description} - Input: {strings}")
+    result = _commonprefix(strings)
+    print("Common prefix:", result)
+
+print_coverage()
+