Test that fit=cover serves a source whose centre is under a pixel wide (part of #282)

An 8192x1 source at 1x8192, or the same turned on its side, has a centre
with the requested proportions 1/8192 of a pixel wide. The crop must keep
at least one pixel of it, or the request fails. The test's cases are now
named by source and requested size.

Model: opus-5-5

internal/imageprocessor/fit_cover_internal_test.go

@@ -9,20 +9,24 @@ import (
 )
 
 // TestImageProcessor_FitCoverServesThinSource verifies that FitCover serves
-// a source of 8192x64 or 8192x1, or one of those turned on its side, at
-// 8192x8192. Scaling such a source to cover that size makes it 128 or 8192
-// times as long as the output on its long side.
+// a thin source at the requested size. A source of 8192x64 or 8192x1 scaled
+// to cover 8192x8192 is 128 or 8192 times as long as the output on its long
+// side. The centre of an 8192x1 source with the proportions of 1x8192 is
+// 1/8192 of a pixel wide. Each case is also turned on its side.
 func TestImageProcessor_FitCoverServesThinSource(t *testing.T) {
 	t.Parallel()
 
 	tests := []struct {
 		name                    string
 		inputWidth, inputHeight int
+		size                    Size
 	}{
-		{"8192x64", 8192, 64},
-		{"8192x1", 8192, 1},
-		{"64x8192", 64, 8192},
-		{"1x8192", 1, 8192},
+		{"8192x64 at 8192x8192", 8192, 64, Size{Width: 8192, Height: 8192}},
+		{"8192x1 at 8192x8192", 8192, 1, Size{Width: 8192, Height: 8192}},
+		{"8192x1 at 1x8192", 8192, 1, Size{Width: 1, Height: 8192}},
+		{"64x8192 at 8192x8192", 64, 8192, Size{Width: 8192, Height: 8192}},
+		{"1x8192 at 8192x8192", 1, 8192, Size{Width: 8192, Height: 8192}},
+		{"1x8192 at 8192x1", 1, 8192, Size{Width: 8192, Height: 1}},
 	}
 
 	for _, tt := range tests {
@@ -33,14 +37,7 @@ func TestImageProcessor_FitCoverServesThinSource(t *testing.T) {
 
 			result, err := New(Params{}).Process(t.Context(),
 				bytes.NewReader(input),
-				&Request{
-					Size: Size{
-						Width:  MaxOutputDimension,
-						Height: MaxOutputDimension,
-					},
-					Format:  FormatJPEG,
-					FitMode: FitCover,
-				})
+				&Request{Size: tt.size, Format: FormatJPEG, FitMode: FitCover})
 			if err != nil {
 				t.Fatalf("Process() error = %v", err)
 			}
@@ -49,11 +46,9 @@ func TestImageProcessor_FitCoverServesThinSource(t *testing.T) {
 
 			t.Logf("Process() made %dx%d", result.Width, result.Height)
 
-			if result.Width != MaxOutputDimension ||
-				result.Height != MaxOutputDimension {
+			if result.Width != tt.size.Width || result.Height != tt.size.Height {
 				t.Errorf("Process() made %dx%d, want %dx%d",
-					result.Width, result.Height,
-					MaxOutputDimension, MaxOutputDimension)
+					result.Width, result.Height, tt.size.Width, tt.size.Height)
 			}
 		})
 	}