pkg/bisect: test a subset of releases

For older bugs (or for bugs on stable trees), our cause bisection
strategy times out while trying to iterate over all reachable tags.

Try to be smarter and only take a subset of them, thus limiting the time
we spend detecting the bug-free release.

Closes #3376.

1 files changed, 59 insertions, 3 deletions

diff --git a/pkg/bisect/bisect_test.go b/pkg/bisect/bisect_test.go
index 600a68b60..d44532fe0 100644
--- a/pkg/bisect/bisect_test.go
+++ b/pkg/bisect/bisect_test.go
@@ -353,9 +353,9 @@ var bisectionTests = []BisectionTest{
 		introduced:  "605",
 		extraTest: func(t *testing.T, res *Result) {
 			// False negative probability of each run is ~35%.
-			// We get two "good" results, so our accumulated confidence is ~42%.
-			assert.Less(t, res.Confidence, 0.5)
-			assert.Greater(t, res.Confidence, 0.4)
+			// We get three "good" results, so our accumulated confidence is ~27%.
+			assert.Less(t, res.Confidence, 0.3)
+			assert.Greater(t, res.Confidence, 0.2)
 		},
 	},
 	// Test bisection returns correct cause with different baseline/config combinations.
@@ -955,3 +955,59 @@ func TestMostFrequentReport(t *testing.T) {
 		})
 	}
 }
+
+func TestPickReleaseTags(t *testing.T) {
+	tests := []struct {
+		name string
+		tags []string
+		ret  []string
+	}{
+		{
+			name: "upstream-clang",
+			tags: []string{
+				"v6.5", "v6.4", "v6.3", "v6.2", "v6.1", "v6.0", "v5.19",
+				"v5.18", "v5.17", "v5.16", "v5.15", "v5.14", "v5.13",
+				"v5.12", "v5.11", "v5.10", "v5.9", "v5.8", "v5.7", "v5.6",
+				"v5.5", "v5.4",
+			},
+			ret: []string{
+				"v6.5", "v6.4", "v6.3", "v6.1", "v5.19", "v5.17", "v5.15",
+				"v5.13", "v5.10", "v5.7", "v5.4",
+			},
+		},
+		{
+			name: "upstream-gcc",
+			tags: []string{
+				"v6.5", "v6.4", "v6.3", "v6.2", "v6.1", "v6.0", "v5.19",
+				"v5.18", "v5.17", "v5.16", "v5.15", "v5.14", "v5.13",
+				"v5.12", "v5.11", "v5.10", "v5.9", "v5.8", "v5.7", "v5.6",
+				"v5.5", "v5.4", "v5.3", "v5.2", "v5.1", "v5.0", "v4.20", "v4.19",
+				"v4.18",
+			},
+			ret: []string{
+				"v6.5", "v6.4", "v6.3", "v6.1", "v5.19", "v5.17", "v5.15",
+				"v5.13", "v5.10", "v5.7", "v5.4", "v5.1", "v4.19", "v4.18",
+			},
+		},
+		{
+			name: "lts",
+			tags: []string{
+				"v5.15.10", "v5.15.9", "v5.15.8", "v5.15.7", "v5.15.6",
+				"v5.15.5", "v5.15.4", "v5.15.3", "v5.15.2", "v5.15.1",
+				"v5.15", "v5.14", "v5.13", "v5.12", "v5.11", "v5.10",
+				"v5.9", "v5.8", "v5.7", "v5.6", "v5.5", "v5.4",
+			},
+			ret: []string{
+				"v5.15.10", "v5.15.9", "v5.15.5", "v5.15", "v5.14", "v5.13",
+				"v5.11", "v5.9", "v5.7", "v5.5", "v5.4",
+			},
+		},
+	}
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			ret := pickReleaseTags(append([]string{}, test.tags...))
+			assert.Equal(t, test.ret, ret)
+		})
+	}
+}