Add expectWithinMargin and test

1 files changed, 26 insertions, 0 deletions

diff --git a/lib/std/testing.zig b/lib/std/testing.zig
index 2d136d56c9..9dca969f45 100644
--- a/lib/std/testing.zig
+++ b/lib/std/testing.zig
@@ -168,6 +168,32 @@ test "expectEqual.union(enum)" {
     expectEqual(a10, a10);
 }
 
+/// This function is intended to be used only in tests. When the actual value is not
+/// within the margin of the expected value,
+/// prints diagnostics to stderr to show exactly how they are not equal, then aborts.
+/// The types must be floating point
+pub fn expectWithinMargin(expected: var, actual: @TypeOf(expected), margin: @TypeOf(expected)) void {
+    std.debug.assert(margin >= 0.0);
+
+    switch (@typeInfo(@TypeOf(actual))) {
+        .Float,
+        .ComptimeFloat,
+        => {
+            if (@fabs(expected - actual) > margin) {
+                std.debug.panic("actual {}, not within margin {} of expected {}", .{ actual, margin, expected });
+            }
+        },
+        else => @compileError("Unable to compare non floating point values"),
+    }
+}
+
+test "expectWithinMargin.f32" {
+    const x: f32 = 12.0;
+    const y: f32 = 12.06;
+
+    expectWithinMargin(x, y, 0.1);
+}
+
 /// This function is intended to be used only in tests. When the two slices are not
 /// equal, prints diagnostics to stderr to show exactly how they are not equal,
 /// then aborts.