diff --git a/test/microwaveprop/workers/nexrad_worker_test.exs b/test/microwaveprop/workers/nexrad_worker_test.exs
new file mode 100644
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+++ b/test/microwaveprop/workers/nexrad_worker_test.exs
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+defmodule Microwaveprop.Workers.NexradWorkerTest do
+  use Microwaveprop.DataCase, async: false
+  use Oban.Testing, repo: Microwaveprop.Repo
+
+  alias Microwaveprop.Radio.Contact
+  alias Microwaveprop.Weather.NexradClient
+  alias Microwaveprop.Weather.NexradObservation
+  alias Microwaveprop.Workers.NexradWorker
+
+  # Build a minimal valid indexed-color PNG (20x20, all-zero pixels).
+  # The worker's PNG decoder only needs:
+  #   - 8-byte signature
+  #   - IHDR (width, height, bit_depth=8, color_type=3)
+  #   - one or more IDAT chunks (zlib-compressed filtered scanlines)
+  #   - IEND
+  # CRCs are read but not validated. Pixel value 0 = no echo everywhere, so
+  # extract_box returns pixel_count: 0 for every point. That's fine: these
+  # tests characterize the worker (filtering, upsert, error handling), not
+  # the PNG decoder (covered in NexradClientTest).
+  defp minimal_png(width \\ 20, height \\ 20) do
+    signature = <<137, 80, 78, 71, 13, 10, 26, 10>>
+    ihdr_data = <<width::32, height::32, 8, 3, 0, 0, 0>>
+    ihdr_chunk = <<byte_size(ihdr_data)::32, "IHDR", ihdr_data::binary, 0::32>>
+
+    # Each scanline: filter byte (0 = None) + width pixel bytes (all 0).
+    raw = for _ <- 1..height, into: <<>>, do: <<0, 0::size(width)-unit(8)>>
+    compressed = :zlib.compress(raw)
+    idat_chunk = <<byte_size(compressed)::32, "IDAT", compressed::binary, 0::32>>
+
+    iend_chunk = <<0::32, "IEND", 0::32>>
+
+    signature <> ihdr_chunk <> idat_chunk <> iend_chunk
+  end
+
+  defp stub_png_success do
+    png = minimal_png()
+
+    Req.Test.stub(NexradClient, fn conn ->
+      Plug.Conn.send_resp(conn, 200, png)
+    end)
+  end
+
+  defp insert_contact!(attrs) do
+    defaults = %{
+      station1: "W5XD",
+      station2: "K5TR",
+      mode: "CW",
+      band: Decimal.new("10000")
+    }
+
+    %Contact{}
+    |> Contact.changeset(Map.merge(defaults, attrs))
+    |> Repo.insert!()
+  end
+
+  describe "perform/1" do
+    test "fetches one n0q frame and upserts one observation per unique snapped point" do
+      stub_png_success()
+
+      # Frame at 14:00 UTC. Two contacts inside the +/-30 min window,
+      # at two distinct positions (snapped to 3-decimal precision).
+      insert_contact!(%{
+        qso_timestamp: ~U[2022-08-20 14:10:00Z],
+        pos1: %{"lat" => 32.9, "lon" => -97.0}
+      })
+
+      insert_contact!(%{
+        qso_timestamp: ~U[2022-08-20 13:45:00Z],
+        pos1: %{"lat" => 33.5, "lon" => -96.5}
+      })
+
+      args = %{
+        "year" => 2022,
+        "month" => 8,
+        "day" => 20,
+        "hour" => 14,
+        "minute" => 0
+      }
+
+      assert :ok = NexradWorker.perform(%Oban.Job{args: args})
+
+      rows = Repo.all(NexradObservation)
+      assert length(rows) == 2
+
+      coords = rows |> Enum.map(&{&1.lat, &1.lon}) |> Enum.sort()
+      assert coords == [{32.9, -97.0}, {33.5, -96.5}]
+
+      for row <- rows do
+        assert DateTime.compare(row.observed_at, ~U[2022-08-20 14:00:00Z]) == :eq
+        assert row.pixel_count == 0
+        assert row.mean_reflectivity_dbz == 0.0
+        assert row.max_reflectivity_dbz == 0.0
+        assert row.texture_variance == 0.0
+      end
+    end
+
+    test "re-running the same job upserts in place (no duplicates, updated fields persist)" do
+      stub_png_success()
+
+      insert_contact!(%{
+        qso_timestamp: ~U[2022-08-20 14:00:00Z],
+        pos1: %{"lat" => 32.9, "lon" => -97.0}
+      })
+
+      args = %{
+        "year" => 2022,
+        "month" => 8,
+        "day" => 20,
+        "hour" => 14,
+        "minute" => 0
+      }
+
+      # First run inserts.
+      assert :ok = NexradWorker.perform(%Oban.Job{args: args})
+      assert [first] = Repo.all(NexradObservation)
+
+      # Seed a stale value on the existing row so we can prove the
+      # second run overwrites it via the ON CONFLICT clause.
+      Repo.update_all(NexradObservation, set: [mean_reflectivity_dbz: 42.0, pixel_count: 999])
+
+      # Second run: same (lat, lon, observed_at) => upsert on the unique
+      # index, not a duplicate insert.
+      assert :ok = NexradWorker.perform(%Oban.Job{args: args})
+
+      assert [second] = Repo.all(NexradObservation)
+      # Unique index kept us at one row.
+      assert second.id == first.id
+      # :replace_all_except [:id, :inserted_at] overwrote the stale values.
+      assert second.mean_reflectivity_dbz == 0.0
+      assert second.pixel_count == 0
+      # inserted_at preserved, updated_at refreshed.
+      assert DateTime.compare(second.inserted_at, first.inserted_at) == :eq
+    end
+
+    test "skips contacts outside the +/- 30 minute window around the frame timestamp" do
+      stub_png_success()
+
+      # Frame at 14:00. Window is [13:30, 14:30].
+      # In-window contact:
+      insert_contact!(%{
+        qso_timestamp: ~U[2022-08-20 14:20:00Z],
+        pos1: %{"lat" => 32.9, "lon" => -97.0}
+      })
+
+      # Out-of-window (too early):
+      insert_contact!(%{
+        qso_timestamp: ~U[2022-08-20 13:00:00Z],
+        pos1: %{"lat" => 40.0, "lon" => -80.0}
+      })
+
+      # Out-of-window (too late):
+      insert_contact!(%{
+        qso_timestamp: ~U[2022-08-20 15:00:00Z],
+        pos1: %{"lat" => 41.0, "lon" => -81.0}
+      })
+
+      # In-window but pos1 is nil — the query filters it out.
+      insert_contact!(%{
+        qso_timestamp: ~U[2022-08-20 14:15:00Z],
+        pos1: nil
+      })
+
+      args = %{"year" => 2022, "month" => 8, "day" => 20, "hour" => 14, "minute" => 0}
+
+      assert :ok = NexradWorker.perform(%Oban.Job{args: args})
+
+      rows = Repo.all(NexradObservation)
+      assert length(rows) == 1
+      assert hd(rows).lat == 32.9
+      assert hd(rows).lon == -97.0
+    end
+
+    test "returns {:error, _} and inserts nothing when upstream returns 404" do
+      insert_contact!(%{
+        qso_timestamp: ~U[2022-08-20 14:00:00Z],
+        pos1: %{"lat" => 32.9, "lon" => -97.0}
+      })
+
+      Req.Test.stub(NexradClient, fn conn ->
+        Plug.Conn.send_resp(conn, 404, "not found")
+      end)
+
+      args = %{"year" => 2022, "month" => 8, "day" => 20, "hour" => 14, "minute" => 0}
+
+      assert {:error, reason} = NexradWorker.perform(%Oban.Job{args: args})
+      assert reason =~ "HTTP 404"
+      assert Repo.aggregate(NexradObservation, :count, :id) == 0
+    end
+
+    test "returns {:error, _} and inserts nothing when the PNG body is garbage" do
+      # A 200 response with bytes that fail the PNG signature match. The
+      # client's decode_png_to_pixels rescues the MatchError and returns
+      # {:error, "PNG decode failed: ..."}; the worker surfaces that.
+      insert_contact!(%{
+        qso_timestamp: ~U[2022-08-20 14:00:00Z],
+        pos1: %{"lat" => 32.9, "lon" => -97.0}
+      })
+
+      Req.Test.stub(NexradClient, fn conn ->
+        Plug.Conn.send_resp(conn, 200, "not a png")
+      end)
+
+      args = %{"year" => 2022, "month" => 8, "day" => 20, "hour" => 14, "minute" => 0}
+
+      assert {:error, reason} = NexradWorker.perform(%Oban.Job{args: args})
+      assert reason =~ "PNG decode failed"
+      assert Repo.aggregate(NexradObservation, :count, :id) == 0
+    end
+
+    test "returns :ok without contacting upstream when no contacts fall in the window" do
+      # Stub that fails loudly if touched.
+      Req.Test.stub(NexradClient, fn _conn ->
+        raise "NexradClient should not be contacted when POI list is empty"
+      end)
+
+      args = %{"year" => 2022, "month" => 8, "day" => 20, "hour" => 14, "minute" => 0}
+
+      assert :ok = NexradWorker.perform(%Oban.Job{args: args})
+      assert Repo.aggregate(NexradObservation, :count, :id) == 0
+    end
+
+    test "defaults the minute arg to 0 when omitted" do
+      stub_png_success()
+
+      insert_contact!(%{
+        qso_timestamp: ~U[2022-08-20 14:05:00Z],
+        pos1: %{"lat" => 32.9, "lon" => -97.0}
+      })
+
+      # No "minute" key — the worker Map.gets it with default 0.
+      args = %{"year" => 2022, "month" => 8, "day" => 20, "hour" => 14}
+
+      assert :ok = NexradWorker.perform(%Oban.Job{args: args})
+
+      assert [row] = Repo.all(NexradObservation)
+      assert DateTime.compare(row.observed_at, ~U[2022-08-20 14:00:00Z]) == :eq
+    end
+
+    test "deduplicates points_of_interest when multiple contacts share a snapped coordinate" do
+      stub_png_success()
+
+      # Two contacts at coordinates that snap to the same 3-decimal point.
+      insert_contact!(%{
+        qso_timestamp: ~U[2022-08-20 14:10:00Z],
+        pos1: %{"lat" => 32.9001, "lon" => -97.0002}
+      })
+
+      insert_contact!(%{
+        qso_timestamp: ~U[2022-08-20 14:20:00Z],
+        pos1: %{"lat" => 32.9004, "lon" => -97.0001}
+      })
+
+      args = %{"year" => 2022, "month" => 8, "day" => 20, "hour" => 14, "minute" => 0}
+
+      assert :ok = NexradWorker.perform(%Oban.Job{args: args})
+
+      # Both snap to (32.900, -97.000) → one row, not two.
+      assert [row] = Repo.all(NexradObservation)
+      assert row.lat == 32.9
+      assert row.lon == -97.0
+    end
+
+    test ~s(accepts legacy pos1 maps that use the "lng" key instead of "lon") do
+      stub_png_success()
+
+      insert_contact!(%{
+        qso_timestamp: ~U[2022-08-20 14:10:00Z],
+        pos1: %{"lat" => 32.9, "lng" => -97.0}
+      })
+
+      args = %{"year" => 2022, "month" => 8, "day" => 20, "hour" => 14, "minute" => 0}
+
+      assert :ok = NexradWorker.perform(%Oban.Job{args: args})
+
+      assert [row] = Repo.all(NexradObservation)
+      assert row.lat == 32.9
+      assert row.lon == -97.0
+    end
+  end
+
+  describe "unique constraint" do
+    test "duplicate enqueues collapse via Oban unique on {year, month, day, hour, minute}" do
+      args = %{
+        "year" => 2022,
+        "month" => 8,
+        "day" => 20,
+        "hour" => 14,
+        "minute" => 0
+      }
+
+      Oban.Testing.with_testing_mode(:manual, fn ->
+        {:ok, job1} = Oban.insert(NexradWorker.new(args))
+        {:ok, job2} = Oban.insert(NexradWorker.new(args))
+
+        # Second insert hits the unique constraint; Oban returns the
+        # existing job instead of inserting a new one.
+        assert job1.id == job2.id
+        assert Repo.aggregate(Oban.Job, :count, :id) == 1
+      end)
+    end
+  end
+end