The `binsearch()` test is somewhat weird in that it doesn't explicitly
spell out its expectations. Instead it does so in a rather ad-hoc way
with some hard-to-understand computations.

Refactor the test to spell out the needle as well as expected index for
all testcases. This refactoring highlights that the `binsearch_func()`
is written somewhat weirdly to find the first integer smaller than the
needle, not smaller or equal to it. Adjust the function accordingly.

While at it, rename the callback function to better convey its meaning.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/basics_test.c | 55 ++++++++++++++++++++++++------------------
 1 file changed, 31 insertions(+), 24 deletions(-)

diff --git a/reftable/basics_test.c b/reftable/basics_test.c
index dc1c87c5df..997c4d9e01 100644
--- a/reftable/basics_test.c
+++ b/reftable/basics_test.c
@@ -12,40 +12,47 @@ license that can be found in the LICENSE file or at
 #include "test_framework.h"
 #include "reftable-tests.h"
 
-struct binsearch_args {
-	int key;
-	int *arr;
+struct integer_needle_lesseq_args {
+	int needle;
+	int *haystack;
 };
 
-static int binsearch_func(size_t i, void *void_args)
+static int integer_needle_lesseq(size_t i, void *_args)
 {
-	struct binsearch_args *args = void_args;
-
-	return args->key < args->arr[i];
+	struct integer_needle_lesseq_args *args = _args;
+	return args->needle <= args->haystack[i];
 }
 
 static void test_binsearch(void)
 {
-	int arr[] = { 2, 4, 6, 8, 10 };
-	size_t sz = ARRAY_SIZE(arr);
-	struct binsearch_args args = {
-		.arr = arr,
+	int haystack[] = { 2, 4, 6, 8, 10 };
+	struct {
+		int needle;
+		size_t expected_idx;
+	} testcases[] = {
+		{-9000, 0},
+		{-1, 0},
+		{0, 0},
+		{2, 0},
+		{3, 1},
+		{4, 1},
+		{7, 3},
+		{9, 4},
+		{10, 4},
+		{11, 5},
+		{9000, 5},
 	};
+	size_t i = 0;
 
-	int i = 0;
-	for (i = 1; i < 11; i++) {
-		size_t res;
-
-		args.key = i;
-		res = binsearch(sz, &binsearch_func, &args);
+	for (i = 0; i < ARRAY_SIZE(testcases); i++) {
+		struct integer_needle_lesseq_args args = {
+			.haystack = haystack,
+			.needle = testcases[i].needle,
+		};
+		size_t idx;
 
-		if (res < sz) {
-			EXPECT(args.key < arr[res]);
-			if (res > 0)
-				EXPECT(args.key >= arr[res - 1]);
-		} else {
-			EXPECT(args.key == 10 || args.key == 11);
-		}
+		idx = binsearch(ARRAY_SIZE(haystack), &integer_needle_lesseq, &args);
+		EXPECT(idx == testcases[i].expected_idx);
 	}
 }
 
-- 
2.44.GIT